Charts

Helm uses a packaging format called charts. A chart is a collection of files that describe a related set of Kubernetes resources. A single chart might be used to deploy something simple, like a memcached pod, or something complex, like a full web app stack with HTTP servers, databases, caches, and so on.

Charts are created as files laid out in a particular directory tree, then they can be packaged into versioned archives to be deployed.

This document explains the chart format, and provides basic guidance for building charts with Helm.

The Chart File Structure

A chart is organized as a collection of files inside of a directory. The directory name is the name of the chart (without versioning information). Thus, a chart describing WordPress would be stored in the wordpress/ directory.

Inside of this directory, Helm will expect a structure that matches this:

wordpress/
  Chart.yaml          # A YAML file containing information about the chart
  LICENSE             # OPTIONAL: A plain text file containing the license for the chart
  README.md           # OPTIONAL: A human-readable README file
  requirements.yaml   # OPTIONAL: A YAML file listing dependencies for the chart
  values.yaml         # The default configuration values for this chart
  charts/             # OPTIONAL: A directory containing any charts upon which this chart depends.
  templates/          # OPTIONAL: A directory of templates that, when combined with values,
                      # will generate valid Kubernetes manifest files.
  templates/NOTES.txt # OPTIONAL: A plain text file containing short usage notes

Helm reserves use of the charts/ and templates/ directories, and of the listed file names. Other files will be left as they are.

The Chart.yaml File

The Chart.yaml file is required for a chart. It contains the following fields:

name: The name of the chart (required)
version: A SemVer 2 version (required)
description: A single-sentence description of this project (optional)
keywords:
  - A list of keywords about this project (optional)
home: The URL of this project's home page (optional)
sources:
  - A list of URLs to source code for this project (optional)
maintainers: # (optional)
  - name: The maintainer's name (required for each maintainer)
    email: The maintainer's email (optional for each maintainer)
engine: gotpl # The name of the template engine (optional, defaults to gotpl)
icon: A URL to an SVG or PNG image to be used as an icon (optional).
appVersion: The version of the app that this contains (optional). This needn't be SemVer.
deprecated: Whether or not this chart is deprecated (optional, boolean)
tillerVersion: The version of Tiller that this chart requires. This should be expressed as a SemVer range: ">2.0.0" (optional)

If you are familiar with the Chart.yaml file format for Helm Classic, you will notice that fields specifying dependencies have been removed. That is because the new Chart format expresses dependencies using the charts/ directory.

Other fields will be silently ignored.

Charts and Versioning

Every chart must have a version number. A version must follow the SemVer 2 standard. Unlike Helm Classic, Kubernetes Helm uses version numbers as release markers. Packages in repositories are identified by name plus version.

For example, an nginx chart whose version field is set to version: 1.2.3 will be named:

nginx-1.2.3.tgz

More complex SemVer 2 names are also supported, such as version: 1.2.3-alpha.1+ef365. But non-SemVer names are explicitly disallowed by the system.

NOTE: Whereas Helm Classic and Deployment Manager were both very GitHub oriented when it came to charts, Kubernetes Helm does not rely upon or require GitHub or even Git. Consequently, it does not use Git SHAs for versioning at all.

The version field inside of the Chart.yaml is used by many of the Helm tools, including the CLI and the Tiller server. When generating a package, the helm package command will use the version that it finds in the Chart.yaml as a token in the package name. The system assumes that the version number in the chart package name matches the version number in the Chart.yaml. Failure to meet this assumption will cause an error.

The appVersion field

Note that the appVersion field is not related to the version field. It is a way of specifying the version of the application. For example, the drupal chart may have an appVersion: 8.2.1, indicating that the version of Drupal included in the chart (by default) is 8.2.1. This field is informational, and has no impact on chart version calculations.

Deprecating Charts

When managing charts in a Chart Repository, it is sometimes necessary to deprecate a chart. The optional deprecated field in Chart.yaml can be used to mark a chart as deprecated. If the latest version of a chart in the repository is marked as deprecated, then the chart as a whole is considered to be deprecated. The chart name can later be reused by publishing a newer version that is not marked as deprecated. The workflow for deprecating charts, as followed by the kubernetes/charts project is: - Update chart’s Chart.yaml to mark the chart as deprecated, bumping the version - Release the new chart version in the Chart Repository - Remove the chart from the source repository (e.g. git)

Chart LICENSE, README and NOTES

Charts can also contain files that describe the installation, configuration, usage and license of a chart. A README for a chart should be formatted in Markdown (README.md), and should generally contain:

  • A description of the application or service the chart provides
  • Any prerequisites or requirements to run the chart
  • Descriptions of options in values.yaml and default values
  • Any other information that may be relevant to the installation or configuration of the chart

The chart can also contain a short plain text templates/NOTES.txt file that will be printed out after installation, and when viewing the status of a release. This file is evaluated as a template, and can be used to display usage notes, next steps, or any other information relevant to a release of the chart. For example, instructions could be provided for connecting to a database, or accessing a web UI. Since this file is printed to STDOUT when running helm install or helm status, it is recommended to keep the content brief and point to the README for greater detail.

Chart Dependencies

In Helm, one chart may depend on any number of other charts. These dependencies can be dynamically linked through the requirements.yaml file or brought in to the charts/ directory and managed manually.

Although manually managing your dependencies has a few advantages some teams need, the preferred method of declaring dependencies is by using a requirements.yaml file inside of your chart.

Note: The dependencies: section of the Chart.yaml from Helm Classic has been completely removed.

Managing Dependencies with requirements.yaml

A requirements.yaml file is a simple file for listing your dependencies.

dependencies:
  - name: apache
    version: 1.2.3
    repository: http://example.com/charts
  - name: mysql
    version: 3.2.1
    repository: http://another.example.com/charts
  • The name field is the name of the chart you want.
  • The version field is the version of the chart you want.
  • The repository field is the full URL to the chart repository. Note that you must also use helm repo add to add that repo locally.

Once you have a dependencies file, you can run helm dependency update and it will use your dependency file to download all of the specified charts into your charts/ directory for you.

$ helm dep up foochart
Hang tight while we grab the latest from your chart repositories...
...Successfully got an update from the "local" chart repository
...Successfully got an update from the "stable" chart repository
...Successfully got an update from the "example" chart repository
...Successfully got an update from the "another" chart repository
Update Complete. Happy Helming!
Saving 2 charts
Downloading apache from repo http://example.com/charts
Downloading mysql from repo http://another.example.com/charts

When helm dependency update retrieves charts, it will store them as chart archives in the charts/ directory. So for the example above, one would expect to see the following files in the charts directory:

charts/
  apache-1.2.3.tgz
  mysql-3.2.1.tgz

Managing charts with requirements.yaml is a good way to easily keep charts updated, and also share requirements information throughout a team.

Alias field in requirements.yaml

In addition to the other fields above, each requirements entry may contain the optional field alias.

Adding an alias for a dependency chart would put a chart in dependencies using alias as name of new dependency.

One can use alias in cases where they need to access a chart with other name(s).

# parentchart/requirements.yaml
dependencies:
  - name: subchart
    repository: http://localhost:10191
    version: 0.1.0
    alias: new-subchart-1
  - name: subchart
    repository: http://localhost:10191
    version: 0.1.0
    alias: new-subchart-2
  - name: subchart
    repository: http://localhost:10191
    version: 0.1.0

In the above example we will get 3 dependencies in all for parentchart

subchart
new-subchart-1
new-subchart-2

The manual way of achieving this is by copy/pasting the same chart in the charts/ directory multiple times with different names.

Tags and Condition fields in requirements.yaml

In addition to the other fields above, each requirements entry may contain the optional fields tags and condition.

All charts are loaded by default. If tags or condition fields are present, they will be evaluated and used to control loading for the chart(s) they are applied to.

Condition - The condition field holds one or more YAML paths (delimited by commas). If this path exists in the top parent’s values and resolves to a boolean value, the chart will be enabled or disabled based on that boolean value. Only the first valid path found in the list is evaluated and if no paths exist then the condition has no effect.

Tags - The tags field is a YAML list of labels to associate with this chart. In the top parent’s values, all charts with tags can be enabled or disabled by specifying the tag and a boolean value.

# parentchart/requirements.yaml
dependencies:
      - name: subchart1
        repository: http://localhost:10191
        version: 0.1.0
        condition: subchart1.enabled, global.subchart1.enabled
        tags:
          - front-end
          - subchart1

      - name: subchart2
        repository: http://localhost:10191
        version: 0.1.0
        condition: subchart2.enabled,global.subchart2.enabled
        tags:
          - back-end
          - subchart1

# parentchart/values.yaml

subchart1:
  enabled: true
tags:
  front-end: false
  back-end: true

In the above example all charts with the tag front-end would be disabled but since the subchart1.enabled path evaluates to ‘true’ in the parent’s values, the condition will override the front-end tag and subchart1 will be enabled.

Since subchart2 is tagged with back-end and that tag evaluates to true, subchart2 will be enabled. Also note that although subchart2 has a condition specified in requirements.yaml, there is no corresponding path and value in the parent’s values so that condition has no effect.

Using the CLI with Tags and Conditions

The --set parameter can be used as usual to alter tag and condition values.

helm install --set tags.front-end=true --set subchart2.enabled=false

Tags and Condition Resolution
  • Conditions (when set in values) always override tags. The first condition path that exists wins and subsequent ones for that chart are ignored.
  • Tags are evaluated as ‘if any of the chart’s tags are true then enable the chart’.
  • Tags and conditions values must be set in the top parent’s values.
  • The tags: key in values must be a top level key. Globals and nested tags: tables are not currently supported.

Importing Child Values via requirements.yaml

In some cases it is desirable to allow a child chart’s values to propagate to the parent chart and be shared as common defaults. An additional benefit of using the exports format is that it will enable future tooling to introspect user-settable values.

The keys containing the values to be imported can be specified in the parent chart’s requirements.yaml file using a YAML list. Each item in the list is a key which is imported from the child chart’s exports field.

To import values not contained in the exports key, use the child/parent format. Examples of both formats are described below.

Using the exports format

If a child chart’s values.yaml file contains an exports field at the root, its contents may be imported directly into the parent’s values by specifying the keys to import as in the example below:

# parent's requirements.yaml file
    ...
    import-values:
      - data
# child's values.yaml file
...
exports:
  data:
    myint: 99

Since we are specifying the key data in our import list, Helm looks in the the exports field of the child chart for data key and imports its contents.

The final parent values would contain our exported field:

# parent's values file
...
myint: 99

Please note the parent key data is not contained in the parent’s final values. If you need to specify the parent key, use the ‘child/parent’ format.

Using the child/parent format

To access values that are not contained in the exports key of the child chart’s values, you will need to specify the source key of the values to be imported (child) and the destination path in the parent chart’s values (parent).

The import-values in the example below instructs Helm to take any values found at child: path and copy them to the parent’s values at the path specified in parent:

# parent's requirements.yaml file
dependencies:
  - name: subchart1
    repository: http://localhost:10191
    version: 0.1.0
    ...
    import-values:
      - child: default.data
        parent: myimports

In the above example, values found at default.data in the subchart1’s values will be imported to the myimports key in the parent chart’s values as detailed below:

# parent's values.yaml file

myimports:
  myint: 0
  mybool: false
  mystring: "helm rocks!"
  
# subchart1's values.yaml file

default:
  data:
    myint: 999
    mybool: true
    

The parent chart’s resulting values would be:

# parent's final values

myimports:
  myint: 999
  mybool: true
  mystring: "helm rocks!"

The parent’s final values now contains the myint and mybool fields imported from subchart1.

Managing Dependencies manually via the charts/ directory

If more control over dependencies is desired, these dependencies can be expressed explicitly by copying the dependency charts into the charts/ directory.

A dependency can be either a chart archive (foo-1.2.3.tgz) or an unpacked chart directory. But its name cannot start with _ or .. Such files are ignored by the chart loader.

For example, if the WordPress chart depends on the Apache chart, the Apache chart (of the correct version) is supplied in the WordPress chart’s charts/ directory:

wordpress:
  Chart.yaml
  requirements.yaml
  # ...
  charts/
    apache/
      Chart.yaml
      # ...
    mysql/
      Chart.yaml
      # ...

The example above shows how the WordPress chart expresses its dependency on Apache and MySQL by including those charts inside of its charts/ directory.

TIP: To drop a dependency into your charts/ directory, use the helm fetch command

Templates and Values

Helm Chart templates are written in the Go template language, with the addition of 50 or so add-on template functions from the Sprig library and a few other specialized functions.

All template files are stored in a chart’s templates/ folder. When Helm renders the charts, it will pass every file in that directory through the template engine.

Values for the templates are supplied two ways:

  • Chart developers may supply a file called values.yaml inside of a chart. This file can contain default values.
  • Chart users may supply a YAML file that contains values. This can be provided on the command line with helm install.

When a user supplies custom values, these values will override the values in the chart’s values.yaml file.

Template Files

Template files follow the standard conventions for writing Go templates (see the text/template Go package documentation for details). An example template file might look something like this:

apiVersion: v1
kind: ReplicationController
metadata:
  name: deis-database
  namespace: deis
  labels:
    heritage: deis
spec:
  replicas: 1
  selector:
    app: deis-database
  template:
    metadata:
      labels:
        app: deis-database
    spec:
      serviceAccount: deis-database
      containers:
        - name: deis-database
          image: {{.Values.imageRegistry}}/postgres:{{.Values.dockerTag}}
          imagePullPolicy: {{.Values.pullPolicy}}
          ports:
            - containerPort: 5432
          env:
            - name: DATABASE_STORAGE
              value: {{default "minio" .Values.storage}}

The above example, based loosely on https://github.com/deis/charts, is a template for a Kubernetes replication controller. It can use the following four template values (usually defined in a values.yaml file):

  • imageRegistry: The source registry for the Docker image.
  • dockerTag: The tag for the docker image.
  • pullPolicy: The Kubernetes pull policy.
  • storage: The storage backend, whose default is set to "minio"

All of these values are defined by the template author. Helm does not require or dictate parameters.

To see many working charts, check out the Kubernetes Charts project

Predefined Values

Values that are supplied via a values.yaml file (or via the --set flag) are accessible from the .Values object in a template. But there are other pre-defined pieces of data you can access in your templates.

The following values are pre-defined, are available to every template, and cannot be overridden. As with all values, the names are case sensitive.

  • Release.Name: The name of the release (not the chart)
  • Release.Time: The time the chart release was last updated. This will match the Last Released time on a Release object.
  • Release.Namespace: The namespace the chart was released to.
  • Release.Service: The service that conducted the release. Usually this is Tiller.
  • Release.IsUpgrade: This is set to true if the current operation is an upgrade or rollback.
  • Release.IsInstall: This is set to true if the current operation is an install.
  • Release.Revision: The revision number. It begins at 1, and increments with each helm upgrade.
  • Chart: The contents of the Chart.yaml. Thus, the chart version is obtainable as Chart.Version and the maintainers are in Chart.Maintainers.
  • Files: A map-like object containing all non-special files in the chart. This will not give you access to templates, but will give you access to additional files that are present. Files can be accessed using {{index .Files "file.name"}} or using the {{.Files.Get name}} or {{.Files.GetString name}} functions. You can also access the contents of the file as []byte using {{.Files.GetBytes}}
  • Capabilities: A map-like object that contains information about the versions of Kubernetes ({{.Capabilities.KubeVersion}}, Tiller ({{.Capabilities.TillerVersion}}, and the supported Kubernetes API versions ({{.Capabilities.APIVersions.Has "batch/v1")

NOTE: Any unknown Chart.yaml fields will be dropped. They will not be accessible inside of the Chart object. Thus, Chart.yaml cannot be used to pass arbitrarily structured data into the template. The values file can be used for that, though.

Values files

Considering the template in the previous section, a values.yaml file that supplies the necessary values would look like this:

imageRegistry: "quay.io/deis"
dockerTag: "latest"
pullPolicy: "Always"
storage: "s3"

A values file is formatted in YAML. A chart may include a default values.yaml file. The Helm install command allows a user to override values by supplying additional YAML values:

$ helm install --values=myvals.yaml wordpress

When values are passed in this way, they will be merged into the default values file. For example, consider a myvals.yaml file that looks like this:

storage: "gcs"

When this is merged with the values.yaml in the chart, the resulting generated content will be:

imageRegistry: "quay.io/deis"
dockerTag: "latest"
pullPolicy: "Always"
storage: "gcs"

Note that only the last field was overridden.

NOTE: The default values file included inside of a chart must be named values.yaml. But files specified on the command line can be named anything.

NOTE: If the --set flag is used on helm install or helm upgrade, those values are simply converted to YAML on the client side.

NOTE: If any required entries in the values file exist, they can be declared as required in the chart template by using the ‘required’ function

Any of these values are then accessible inside of templates using the .Values object:

apiVersion: v1
kind: ReplicationController
metadata:
  name: deis-database
  namespace: deis
  labels:
    heritage: deis
spec:
  replicas: 1
  selector:
    app: deis-database
  template:
    metadata:
      labels:
        app: deis-database
    spec:
      serviceAccount: deis-database
      containers:
        - name: deis-database
          image: {{.Values.imageRegistry}}/postgres:{{.Values.dockerTag}}
          imagePullPolicy: {{.Values.pullPolicy}}
          ports:
            - containerPort: 5432
          env:
            - name: DATABASE_STORAGE
              value: {{default "minio" .Values.storage}}

Scope, Dependencies, and Values

Values files can declare values for the top-level chart, as well as for any of the charts that are included in that chart’s charts/ directory. Or, to phrase it differently, a values file can supply values to the chart as well as to any of its dependencies. For example, the demonstration WordPress chart above has both mysql and apache as dependencies. The values file could supply values to all of these components:

title: "My WordPress Site" # Sent to the WordPress template

mysql:
  max_connections: 100 # Sent to MySQL
  password: "secret"

apache:
  port: 8080 # Passed to Apache

Charts at a higher level have access to all of the variables defined beneath. So the WordPress chart can access the MySQL password as .Values.mysql.password. But lower level charts cannot access things in parent charts, so MySQL will not be able to access the title property. Nor, for that matter, can it access apache.port.

Values are namespaced, but namespaces are pruned. So for the WordPress chart, it can access the MySQL password field as .Values.mysql.password. But for the MySQL chart, the scope of the values has been reduced and the namespace prefix removed, so it will see the password field simply as .Values.password.

Global Values

As of 2.0.0-Alpha.2, Helm supports special “global” value. Consider this modified version of the previous example:

title: "My WordPress Site" # Sent to the WordPress template

global:
  app: MyWordPress

mysql:
  max_connections: 100 # Sent to MySQL
  password: "secret"

apache:
  port: 8080 # Passed to Apache

The above adds a global section with the value app: MyWordPress. This value is available to all charts as .Values.global.app.

For example, the mysql templates may access app as {{.Values.global.app}}, and so can the apache chart. Effectively, the values file above is regenerated like this:

title: "My WordPress Site" # Sent to the WordPress template

global:
  app: MyWordPress

mysql:
  global:
    app: MyWordPress
  max_connections: 100 # Sent to MySQL
  password: "secret"

apache:
  global:
    app: MyWordPress
  port: 8080 # Passed to Apache

This provides a way of sharing one top-level variable with all subcharts, which is useful for things like setting metadata properties like labels.

If a subchart declares a global variable, that global will be passed downward (to the subchart’s subcharts), but not upward to the parent chart. There is no way for a subchart to influence the values of the parent chart.

Also, global variables of parent charts take precedence over the global variables from subcharts.

References

When it comes to writing templates and values files, there are several standard references that will help you out.

Using Helm to Manage Charts

The helm tool has several commands for working with charts.

It can create a new chart for you:

$ helm create mychart
Created mychart/

Once you have edited a chart, helm can package it into a chart archive for you:

$ helm package mychart
Archived mychart-0.1.-.tgz

You can also use helm to help you find issues with your chart’s formatting or information:

$ helm lint mychart
No issues found

Chart Repositories

A chart repository is an HTTP server that houses one or more packaged charts. While helm can be used to manage local chart directories, when it comes to sharing charts, the preferred mechanism is a chart repository.

Any HTTP server that can serve YAML files and tar files and can answer GET requests can be used as a repository server.

Helm comes with built-in package server for developer testing (helm serve). The Helm team has tested other servers, including Google Cloud Storage with website mode enabled, and S3 with website mode enabled.

A repository is characterized primarily by the presence of a special file called index.yaml that has a list of all of the packages supplied by the repository, together with metadata that allows retrieving and verifying those packages.

On the client side, repositories are managed with the helm repo commands. However, Helm does not provide tools for uploading charts to remote repository servers. This is because doing so would add substantial requirements to an implementing server, and thus raise the barrier for setting up a repository.

Chart Starter Packs

The helm create command takes an optional --starter option that lets you specify a “starter chart”.

Starters are just regular charts, but are located in $HELM_HOME/starters. As a chart developer, you may author charts that are specifically designed to be used as starters. Such charts should be designed with the following considerations in mind:

  • The Chart.yaml will be overwritten by the generator.
  • Users will expect to modify such a chart’s contents, so documentation should indicate how users can do so.

Currently the only way to add a chart to $HELM_HOME/starters is to manually copy it there. In your chart’s documentation, you may want to explain that process.

+++ aliases = [ “charts_hooks.md”, “docs/charts_hooks.md”, “using_helm/charts_hooks.md”, “developing_charts/charts_hooks.md” ] +++

Hooks

Helm provides a hook mechanism to allow chart developers to intervene at certain points in a release’s life cycle. For example, you can use hooks to:

  • Load a ConfigMap or Secret during install before any other charts are loaded.
  • Execute a Job to back up a database before installing a new chart, and then execute a second job after the upgrade in order to restore data.
  • Run a Job before deleting a release to gracefully take a service out of rotation before removing it.

Hooks work like regular templates, but they have special annotations that cause Helm to utilize them differently. In this section, we cover the basic usage pattern for hooks.

The Available Hooks

The following hooks are defined:

  • pre-install: Executes after templates are rendered, but before any resources are created in Kubernetes.
  • post-install: Executes after all resources are loaded into Kubernetes
  • pre-delete: Executes on a deletion request before any resources are deleted from Kubernetes.
  • post-delete: Executes on a deletion request after all of the release’s resources have been deleted.
  • pre-upgrade: Executes on an upgrade request after templates are rendered, but before any resources are loaded into Kubernetes (e.g. before a Kubernetes apply operation).
  • post-upgrade: Executes on an upgrade after all resources have been upgraded.
  • pre-rollback: Executes on a rollback request after templates are rendered, but before any resources have been rolled back.
  • post-rollback: Executes on a rollback request after all resources have been modified.

Hooks and the Release Lifecycle

Hooks allow you, the chart developer, an opportunity to perform operations at strategic points in a release lifecycle. For example, consider the lifecycle for a helm install. By default, the lifecycle looks like this:

  1. User runs helm install foo
  2. Chart is loaded into Tiller
  3. After some verification, Tiller renders the foo templates
  4. Tiller loads the resulting resources into Kubernetes
  5. Tiller returns the release name (and other data) to the client
  6. The client exits

Helm defines two hooks for the install lifecycle: pre-install and post-install. If the developer of the foo chart implements both hooks, the lifecycle is altered like this:

  1. User runs helm install foo
  2. Chart is loaded into Tiller
  3. After some verification, Tiller renders the foo templates
  4. Tiller prepares to execute the pre-install hooks (loading hook resources into Kubernetes)
  5. Tiller sorts hooks by weight (assigning a weight of 0 by default) and by name for those hooks with the same weight in ascending order.
  6. Tiller then loads the hook with the lowest weight first (negative to positive)
  7. Tiller waits until the hook is “Ready”
  8. Tiller loads the resulting resources into Kubernetes. Note that if the --wait flag is set, Tiller will wait until all resources are in a ready state and will not run the post-install hook until they are ready.
  9. Tiller executes the post-install hook (loading hook resources)
  10. Tiller waits until the hook is “Ready”
  11. Tiller returns the release name (and other data) to the client
  12. The client exits

What does it mean to wait until a hook is ready? This depends on the resource declared in the hook. If the resources is a Job kind, Tiller will wait until the job successfully runs to completion. And if the job fails, the release will fail. This is a blocking operation, so the Helm client will pause while the Job is run.

For all other kinds, as soon as Kubernetes marks the resource as loaded (added or updated), the resource is considered “Ready”. When many resources are declared in a hook, the resources are executed serially. If they have hook weights (see below), they are executed in weighted order. Otherwise, ordering is not guaranteed. (In Helm 2.3.0 and after, they are sorted alphabetically. That behavior, though, is not considered binding and could change in the future.) It is considered good practice to add a hook weight, and set it to 0 if weight is not important.

Hook resources are not managed with corresponding releases

The resources that a hook creates are not tracked or managed as part of the release. Once Tiller verifies that the hook has reached its ready state, it will leave the hook resource alone.

Practically speaking, this means that if you create resources in a hook, you cannot rely upon helm delete to remove the resources. To destroy such resources, you need to either write code to perform this operation in a pre-delete or post-delete hook or add "helm.sh/hook-delete-policy" annotation to the hook template file.

Writing a Hook

Hooks are just Kubernetes manifest files with special annotations in the metadata section. Because they are template files, you can use all of the normal template features, including reading .Values, .Release, and .Template.

For example, this template, stored in templates/post-install-job.yaml, declares a job to be run on post-install:

apiVersion: batch/v1
kind: Job
metadata:
  name: "{{.Release.Name}}"
  labels:
    heritage: {{.Release.Service | quote }}
    release: {{.Release.Name | quote }}
    chart: "{{.Chart.Name}}-{{.Chart.Version}}"
  annotations:
    # This is what defines this resource as a hook. Without this line, the
    # job is considered part of the release.
    "helm.sh/hook": post-install
    "helm.sh/hook-weight": "-5"
    "helm.sh/hook-delete-policy": hook-succeeded
spec:
  template:
    metadata:
      name: "{{.Release.Name}}"
      labels:
        heritage: {{.Release.Service | quote }}
        release: {{.Release.Name | quote }}
        chart: "{{.Chart.Name}}-{{.Chart.Version}}"
    spec:
      restartPolicy: Never
      containers:
      - name: post-install-job
        image: "alpine:3.3"
        command: ["/bin/sleep","{{default "10" .Values.sleepyTime}}"]

What makes this template a hook is the annotation:

  annotations:
    "helm.sh/hook": post-install

One resource can implement multiple hooks:

  annotations:
    "helm.sh/hook": post-install,post-upgrade

Similarly, there is no limit to the number of different resources that may implement a given hook. For example, one could declare both a secret and a config map as a pre-install hook.

When subcharts declare hooks, those are also evaluated. There is no way for a top-level chart to disable the hooks declared by subcharts.

It is possible to define a weight for a hook which will help build a deterministic executing order. Weights are defined using the following annotation:

  annotations:
    "helm.sh/hook-weight": "5"

Hook weights can be positive or negative numbers but must be represented as strings. When Tiller starts the execution cycle of hooks of a particular Kind it will sort those hooks in ascending order.

It is also possible to define policies that determine when to delete corresponding hook resources. Hook deletion policies are defined using the following annotation:

  annotations:
    "helm.sh/hook-delete-policy": hook-succeeded

When using "helm.sh/hook-delete-policy" annotation, you can choose its value from "hook-succeeded" and "hook-failed". The value "hook-succeeded" specifies Tiller should delete the hook after the hook is successfully executed, while the value "hook-failed"specifies Tiller should delete the hook if the hook failed during execution.

+++ aliases = [ “chart-development-tips-and-tricks.md”, “docs/chart-development-tips-and-tricks.md”, “using_helm/chart-development-tips-and-tricks.md”, “developing_charts/chart-development-tips-and-tricks.md” ] +++

Chart Development Tips and Tricks

This guide covers some of the tips and tricks Helm chart developers have learned while building production-quality charts.

Know Your Template Functions

Helm uses Go templates for templating your resource files. While Go ships several built-in functions, we have added many others.

First, we added almost all of the functions in the Sprig library. We removed two for security reasons: env and expandenv (which would have given chart authors access to Tiller’s environment).

We also added two special template functions: include and required. The include function allows you to bring in another template, and then pass the results to other template functions.

For example, this template snippet includes a template called mytpl.tpl, then lowercases the result, then wraps that in double quotes.

value: {{include "mytpl.tpl" . | lower | quote}}

The required function allows you to declare a particular values entry as required for template rendering. If the value is empty, the template rendering will fail with a user submitted error message.

The following example of the required function declares an entry for .Values.who is required, and will print an error message when that entry is missing:

value: {{required "A valid .Values.who entry required!" .Values.who }}

Quote Strings, Don’t Quote Integers

When you are working with string data, you are always safer quoting the strings than leaving them as bare words:

name: {{.Values.MyName | quote }}

But when working with integers do not quote the values. That can, in many cases, cause parsing errors inside of Kubernetes.

port: {{ .Values.Port }}

Using the ‘include’ Function

Go provides a way of including one template in another using a built-in template directive. However, the built-in function cannot be used in Go template pipelines.

To make it possible to include a template, and then perform an operation on that template’s output, Helm has a special include function:

{{ include "toYaml" $value | indent 2 }}

The above includes a template called toYaml, passes it $value, and then passes the output of that template to the indent function.

Because YAML ascribes significance to indentation levels and whitespace, this is one great way to include snippets of code, but handle indentation in a relevant context.

Using the ‘required’ function

Go provides a way for setting template options to control behavior when a map is indexed with a key that’s not present in the map. This is typically set with template.Options(“missingkey=option”), where option can be default, zero, or error. While setting this option to error will stop execution with an error, this would apply to every missing key in the map. There may be situations where a chart developer wants to enforce this behavior for select values in the values.yml file.

The required function gives developers the ability to declare a value entry as required for template rendering. If the entry is empty in values.yml, the template will not render and will return an error message supplied by the developer.

For example:

{{ required "A valid foo is required!" .Values.foo }}

The above will render the template when .Values.foo is defined, but will fail to render and exit when .Values.foo is undefined.

Automatically Roll Deployments When ConfigMaps or Secrets change

Often times configmaps or secrets are injected as configuration files in containers. Depending on the application a restart may be required should those be updated with a subsequent helm upgrade, but if the deployment spec itself didn’t change the application keeps running with the old configuration resulting in an inconsistent deployment.

The sha256sum function can be used together with the include function to ensure a deployments template section is updated if another spec changes:

kind: Deployment
spec:
  template:
    metadata:
      annotations:
        checksum/config: {{ include (print $.Template.BasePath "/secret.yaml") . | sha256sum }}
[...]

Tell Tiller Not To Delete a Resource

Sometimes there are resources that should not be deleted when Helm runs a helm delete. Chart developers can add an annotation to a resource to prevent it from being deleted.

kind: Secret
metadata:
  annotations:
    "helm.sh/resource-policy": keep
[...]

(Quotation marks are required)

The annotation "helm.sh/resource-policy": keep instructs Tiller to skip this resource during a helm delete operation. However, this resource becomes orphaned. Helm will no longer manage it in any way. This can lead to problems if using helm install --replace on a release that has already been deleted, but has kept resources.

Using “Partials” and Template Includes

Sometimes you want to create some reusable parts in your chart, whether they’re blocks or template partials. And often, it’s cleaner to keep these in their own files.

In the templates/ directory, any file that begins with an underscore(_) is not expected to output a Kubernetes manifest file. So by convention, helper templates and partials are placed in a _helpers.tpl file.

Complex Charts with Many Dependencies

Many of the charts in the official charts repository are “building blocks” for creating more advanced applications. But charts may be used to create instances of large-scale applications. In such cases, a single umbrella chart may have multiple subcharts, each of which functions as a piece of the whole.

The current best practice for composing a complex application from discrete parts is to create a top-level umbrella chart that exposes the global configurations, and then use the charts/ subdirectory to embed each of the components.

Two strong design patterns are illustrated by these projects:

SAP’s OpenStack chart: This chart installs a full OpenStack IaaS on Kubernetes. All of the charts are collected together in one GitHub repository.

Deis’s Workflow: This chart exposes the entire Deis PaaS system with one chart. But it’s different from the SAP chart in that this master chart is built from each component, and each component is tracked in a different Git repository. Check out the requirements.yaml file to see how this chart is composed by their CI/CD pipeline.

Both of these charts illustrate proven techniques for standing up complex environments using Helm.

YAML is a Superset of JSON

According to the YAML specification, YAML is a superset of JSON. That means that any valid JSON structure ought to be valid in YAML.

This has an advantage: Sometimes template developers may find it easier to express a datastructure with a JSON-like syntax rather than deal with YAML’s whitespace sensitivity.

As a best practice, templates should follow a YAML-like syntax unless the JSON syntax substantially reduces the risk of a formatting issue.

Be Careful with Generating Random Values

There are functions in Helm that allow you to generate random data, cryptographic keys, and so on. These are fine to use. But be aware that during upgrades, templates are re-executed. When a template run generates data that differs from the last run, that will trigger an update of that resource.

+++ aliases = [ “developing_charts.md”, “docs/developing_charts.md”, “using_helm/developing_charts.md”, “developing_charts/developing_charts.md” ] +++

The Chart Repository Guide

This section explains how to create and work with Helm chart repositories. At a high level, a chart repository is a location where packaged charts can be stored and shared.

The official chart repository is maintained by the Kubernetes Charts, and we welcome participation. But Helm also makes it easy to create and run your own chart repository. This guide explains how to do so.

Prerequisites

Create a chart repository

A chart repository is an HTTP server that houses an index.yaml file and optionally some packaged charts. When you’re ready to share your charts, the preferred way to do so is by uploading them to a chart repository.

Note: For Helm 2.0.0, chart repositories do not have any intrinsic authentication. There is an issue tracking progress in GitHub.

Because a chart repository can be any HTTP server that can serve YAML and tar files and can answer GET requests, you have a plethora of options when it comes down to hosting your own chart repository. For example, you can use a Google Cloud Storage (GCS) bucket, Amazon S3 bucket, Github Pages, or even create your own web server.

The chart repository structure

A chart repository consists of packaged charts and a special file called index.yaml which contains an index of all of the charts in the repository. Frequently, the charts that index.yaml describes are also hosted on the same server, as are the provenance files.

For example, the layout of the repository https://example.com/charts might look like this:

charts/
  |
  |- index.yaml
  |
  |- alpine-0.1.2.tgz
  |
  |- alpine-0.1.2.tgz.prov

In this case, the index file would contain information about one chart, the Alpine chart, and provide the download URL https://example.com/charts/alpine-0.1.2.tgz for that chart.

It is not required that a chart package be located on the same server as the index.yaml file. However, doing so is often the easiest.

The index file

The index file is a yaml file called index.yaml. It contains some metadata about the package, including the contents of a chart’s Chart.yaml file. A valid chart repository must have an index file. The index file contains information about each chart in the chart repository. The helm repo index command will generate an index file based on a given local directory that contains packaged charts.

This is an example of an index file:

apiVersion: v1
entries:
  alpine:
    - created: 2016-10-06T16:23:20.499814565-06:00
      description: Deploy a basic Alpine Linux pod
      digest: 99c76e403d752c84ead610644d4b1c2f2b453a74b921f422b9dcb8a7c8b559cd
      home: https://k8s.io/helm
      name: alpine
      sources:
      - https://github.com/kubernetes/helm
      urls:
      - https://technosophos.github.io/tscharts/alpine-0.2.0.tgz
      version: 0.2.0
    - created: 2016-10-06T16:23:20.499543808-06:00
      description: Deploy a basic Alpine Linux pod
      digest: 515c58e5f79d8b2913a10cb400ebb6fa9c77fe813287afbacf1a0b897cd78727
      home: https://k8s.io/helm
      name: alpine
      sources:
      - https://github.com/kubernetes/helm
      urls:
      - https://technosophos.github.io/tscharts/alpine-0.1.0.tgz
      version: 0.1.0
  nginx:
    - created: 2016-10-06T16:23:20.499543808-06:00
      description: Create a basic nginx HTTP server
      digest: aaff4545f79d8b2913a10cb400ebb6fa9c77fe813287afbacf1a0b897cdffffff
      home: https://k8s.io/helm
      name: nginx
      sources:
      - https://github.com/kubernetes/charts
      urls:
      - https://technosophos.github.io/tscharts/nginx-1.1.0.tgz
      version: 1.1.0
generated: 2016-10-06T16:23:20.499029981-06:00

A generated index and packages can be served from a basic webserver. You can test things out locally with the helm serve command, which starts a local server.

$ helm serve --repo-path ./charts
Regenerating index. This may take a moment.
Now serving you on 127.0.0.1:8879

The above starts a local webserver, serving the charts it finds in ./charts. The serve command will automatically generate an index.yaml file for you during startup.

Hosting Chart Repositories

This part shows several ways to serve a chart repository.

Google Cloud Storage

The first step is to create your GCS bucket. We’ll call ours fantastic-charts.

Create a GCS Bucket

Next, make your bucket public by editing the bucket permissions.

Edit Permissions

Insert this line item to make your bucket public:

Make Bucket Public

Congratulations, now you have an empty GCS bucket ready to serve charts!

You may upload your chart repository using the Google Cloud Storage command line tool, or using the GCS web UI. This is the technique the official Kubernetes Charts repository hosts its charts, so you may want to take a peek at that project if you get stuck.

Note: A public GCS bucket can be accessed via simple HTTPS at this address https://bucket-name.storage.googleapis.com/.

Github Pages example

In a similar way you can create charts repository using GitHub Pages.

GitHub allows you to serve static web pages in two different ways:

  • By configuring a project to serve the contents of its docs/ directory
  • By configuring a project to serve a particular branch

We’ll take the second approach, though the first is just as easy.

The first step will be to create your gh-pages branch. You can do that locally as.

$ git checkout -b gh-pages

Or via web browser using Branch button on your Github repository:

Create Github Pages branch

Next, you’ll want to make sure your gh-pages branch is set as Github Pages, click on your repo Settings and scroll down to Github pages section and set as per below:

Create Github Pages branch

By default Source usually gets set to gh-pages branch. If this is not set by default, then select it.

You can use a custom domain there if you wish so.

And check that Enforce HTTPS is ticked, so the HTTPS will be used when charts are served.

In such setup you can use master branch to store your charts code, and gh-pages branch as charts repository, e.g.: https://USERNAME.github.io/REPONAME. The demonstration TS Charts repository is accessible at https://technosophos.github.io/tscharts/.

Ordinary web servers

To configure an ordinary web server to serve Helm charts, you merely need to do the following:

  • Put your index and charts in a directory that the server can serve
  • Make sure the index.yaml file can be accessed with no authentication requirement
  • Make sure yaml files are served with the correct content type (text/yaml or text/x-yaml)

For example, if you want to serve your charts out of $WEBROOT/charts, make sure there is a charts/ directory in your web root, and put the index file and charts inside of that folder.

Managing Chart Repositories

Now that you have a chart repository, the last part of this guide explains how to maintain charts in that repository.

Store charts in your chart repository

Now that you have a chart repository, let’s upload a chart and an index file to the repository. Charts in a chart repository must be packaged (helm package chart-name/) and versioned correctly (following SemVer 2 guidelines).

These next steps compose an example workflow, but you are welcome to use whatever workflow you fancy for storing and updating charts in your chart repository.

Once you have a packaged chart ready, create a new directory, and move your packaged chart to that directory.

$ helm package docs/examples/alpine/
$ mkdir fantastic-charts
$ mv alpine-0.1.0.tgz fantastic-charts/
$ helm repo index fantastic-charts --url https://fantastic-charts.storage.googleapis.com

The last command takes the path of the local directory that you just created and the URL of your remote chart repository and composes an index.yaml file inside the given directory path.

Now you can upload the chart and the index file to your chart repository using a sync tool or manually. If you’re using Google Cloud Storage, check out this example workflow using the gsutil client. For GitHub, you can simply put the charts in the appropriate destination branch.

Add new charts to an existing repository

Each time you want to add a new chart to your repository, you must regenerate the index. The helm repo index command will completely rebuild the index.yaml file from scratch, including only the charts that it finds locally.

However, you can use the --merge flag to incrementally add new charts to an existing index.yaml file (a great option when working with a remote repository like GCS). Run helm repo index --help to learn more,

Make sure that you upload both the revised index.yaml file and the chart. And if you generated a provenance file, upload that too.

Share your charts with others

When you’re ready to share your charts, simply let someone know what the URL of your repository is.

From there, they will add the repository to their helm client via the helm repo add [NAME] [URL] command with any name they would like to use to reference the repository.

$ helm repo add fantastic-charts https://fantastic-charts.storage.googleapis.com
$ helm repo list
fantastic-charts    https://fantastic-charts.storage.googleapis.com

If the charts are backed by HTTP basic authentication, you can also supply the username and password here:

$ helm repo add fantastic-charts https://username:[email protected]
$ helm repo list
fantastic-charts    https://username:[email protected]

Note: A repository will not be added if it does not contain a valid index.yaml.

After that, your users will be able to search through your charts. After you’ve updated the repository, they can use the helm repo update command to get the latest chart information.

Under the hood, the helm repo add and helm repo update commands are fetching the index.yaml file and storing them in the $HELM_HOME/repository/cache/ directory. This is where the helm search function finds information about charts.

+++ aliases = [ “developing_charts_sync_example.md”, “docs/developing_charts_sync_example.md”, “using_helm/developing_charts_sync_example.md”, “developing_charts/developing_charts_sync_example.md” ] +++

Syncing Your Chart Repository

Note: This example is specifically for a Google Cloud Storage (GCS) bucket which serves a chart repository.

Prerequisites

  • Install the gsutil tool. We rely heavily on the gsutil rsync functionality
  • Be sure to have access to the helm binary
  • _Optional: We recommend you set object versioning on your GCS bucket in case you accidentally delete something._

Set up a local chart repository directory

Create a local directory like we did in the chart repository guide, and place your packaged charts in that directory.

For example:

$ mkdir fantastic-charts
$ mv alpine-0.1.0.tgz fantastic-charts/

Generate an updated index.yaml

Use helm to generate an updated index.yaml file by passing in the directory path and the url of the remote repository to the helm repo index command like this:

$ helm repo index fantastic-charts/ --url https://fantastic-charts.storage.googleapis.com

This will generate an updated index.yaml file and place in the fantastic-charts/ directory.

Sync your local and remote chart repositories

Upload the contents of the directory to your GCS bucket by running scripts/sync-repo.sh and pass in the local directory name and the GCS bucket name.

For example:

$ pwd
/Users/funuser/go/src/github.com/kubernetes/helm
$ scripts/sync-repo.sh fantastic-charts/ fantastic-charts
Getting ready to sync your local directory (fantastic-charts/) to a remote repository at gs://fantastic-charts
Verifying Prerequisites....
Thumbs up! Looks like you have gsutil. Let's continue.
Building synchronization state...
Starting synchronization
Would copy file://fantastic-charts/alpine-0.1.0.tgz to gs://fantastic-charts/alpine-0.1.0.tgz
Would copy file://fantastic-charts/index.yaml to gs://fantastic-charts/index.yaml
Are you sure you would like to continue with these changes?? [y/N]} y
Building synchronization state...
Starting synchronization
Copying file://fantastic-charts/alpine-0.1.0.tgz [Content-Type=application/x-tar]...
Uploading   gs://fantastic-charts/alpine-0.1.0.tgz:              740 B/740 B
Copying file://fantastic-charts/index.yaml [Content-Type=application/octet-stream]...
Uploading   gs://fantastic-charts/index.yaml:                    347 B/347 B
Congratulations your remote chart repository now matches the contents of fantastic-charts/

Updating your chart repository

You’ll want to keep a local copy of the contents of your chart repository or use gsutil rsync to copy the contents of your remote chart repository to a local directory.

For example:

$ gsutil rsync -d -n gs://bucket-name local-dir/    # the -n flag does a dry run
Building synchronization state...
Starting synchronization
Would copy gs://bucket-name/alpine-0.1.0.tgz to file://local-dir/alpine-0.1.0.tgz
Would copy gs://bucket-name/index.yaml to file://local-dir/index.yaml

$ gsutil rsync -d gs://bucket-name local-dir/       # performs the copy actions
Building synchronization state...
Starting synchronization
Copying gs://bucket-name/alpine-0.1.0.tgz...
Downloading file://local-dir/alpine-0.1.0.tgz:                        740 B/740 B
Copying gs://bucket-name/index.yaml...
Downloading file://local-dir/index.yaml:                              346 B/346 B

Helpful Links: * Documentation on gsutil rsync * The Chart Repository Guide * Documentation on object versioning and concurrency control in Google Cloud Storage

+++ aliases = [ “provenance.md”, “docs/provenance.md”, “using_helm/provenance.md”, “developing_charts/provenance.md” ] +++

Helm Provenance and Integrity

Helm has provenance tools which help chart users verify the integrity and origin of a package. Using industry-standard tools based on PKI, GnuPG, and well-respected package managers, Helm can generate and verify signature files.

Note: Version 2.0.0-alpha.4 introduced a system for verifying the authenticity of charts. While we do not anticipate that any major changes will be made to the file formats or provenancing algorithms, this portion of Helm is not considered frozen until 2.0.0-RC1 is released. The original plan for this feature can be found at issue 983.

Overview

Integrity is established by comparing a chart to a provenance record. Provenance records are stored in provenance files, which are stored alongside a packaged chart. For example, if a chart is named myapp-1.2.3.tgz, its provenance file will be myapp-1.2.3.tgz.prov.

Provenance files are generated at packaging time (helm package --sign ...), and can be checked by multiple commands, notable helm install --verify.

The Workflow

This section describes a potential workflow for using provenance data effectively.

Prerequisites:

  • A valid PGP keypair in a binary (not ASCII-armored) format
  • The helm command line tool
  • GnuPG command line tools (optional)
  • Keybase command line tools (optional)

NOTE: If your PGP private key has a passphrase, you will be prompted to enter that passphrase for any commands that support the --sign option.

Creating a new chart is the same as before:

$ helm create mychart
Creating mychart

Once ready to package, add the --sign flag to helm package. Also, specify the name under which the signing key is known and the keyring containing the corresponding private key:

$ helm package --sign --key 'helm signing key' --keyring path/to/keyring.secret mychart

TIP: for GnuPG users, your secret keyring is in ~/.gnupg/secring.gpg. You can use gpg --list-secret-keys to list the keys you have.

At this point, you should see both mychart-0.1.0.tgz and mychart-0.1.0.tgz.prov. Both files should eventually be uploaded to your desired chart repository.

You can verify a chart using helm verify:

$ helm verify mychart-0.1.0.tgz

A failed verification looks like this:

$ helm verify topchart-0.1.0.tgz
Error: sha256 sum does not match for topchart-0.1.0.tgz: "sha256:1939fbf7c1023d2f6b865d137bbb600e0c42061c3235528b1e8c82f4450c12a7" != "sha256:5a391a90de56778dd3274e47d789a2c84e0e106e1a37ef8cfa51fd60ac9e623a"

To verify during an install, use the --verify flag.

$ helm install --verify mychart-0.1.0.tgz

If the keyring (containing the public key associated with the signed chart) is not in the default location, you may need to point to the keyring with --keyring PATH as in the helm package example.

If verification fails, the install will be aborted before the chart is even pushed up to Tiller.

Using Keybase.io credentials

The Keybase.io service makes it easy to establish a chain of trust for a cryptographic identity. Keybase credentials can be used to sign charts.

Prerequisites:

  • A configured Keybase.io account
  • GnuPG installed locally
  • The keybase CLI installed locally

Signing packages

The first step is to import your keybase keys into your local GnuPG keyring:

$ keybase pgp export -s | gpg --import

This will convert your Keybase key into the OpenPGP format, and then import it locally into your ~/.gnupg/secring.gpg file.

You can double check by running gpg --list-secret-keys.

$ gpg --list-secret-keys                                                                                                       1 ↵
/Users/mattbutcher/.gnupg/secring.gpg
-------------------------------------
sec   2048R/1FC18762 2016-07-25
uid                  technosophos (keybase.io/technosophos) <[email protected]>
ssb   2048R/D125E546 2016-07-25

Note that your secret key will have an identifier string:

technosophos (keybase.io/technosophos) <[email protected]>

That is the full name of your key.

Next, you can package and sign a chart with helm package. Make sure you use at least part of that name string in --key.

$ helm package --sign --key technosophos --keyring ~/.gnupg/secring.gpg mychart

As a result, the package command should produce both a .tgz file and a .tgz.prov file.

Verifying packages

You can also use a similar technique to verify a chart signed by someone else’s Keybase key. Say you want to verify a package signed by keybase.io/technosophos. To do this, use the keybase tool:

$ keybase follow technosophos
$ keybase pgp pull

The first command above tracks the user technosophos. Next keybase pgp pull downloads the OpenPGP keys of all of the accounts you follow, placing them in your GnuPG keyring (~/.gnupg/pubring.gpg).

At this point, you can now use helm verify or any of the commands with a --verify flag:

$ helm verify somechart-1.2.3.tgz

Reasons a chart may not verify

These are common reasons for failure.

  • The prov file is missing or corrupt. This indicates that something is misconfigured or that the original maintainer did not create a provenance file.
  • The key used to sign the file is not in your keyring. This indicate that the entity who signed the chart is not someone you’ve already signaled that you trust.
  • The verification of the prov file failed. This indicates that something is wrong with either the chart or the provenance data.
  • The file hashes in the provenance file do not match the hash of the archive file. This indicates that the archive has been tampered with.

If a verification fails, there is reason to distrust the package.

The Provenance File

The provenance file contains a chart’s YAML file plus several pieces of verification information. Provenance files are designed to be automatically generated.

The following pieces of provenance data are added:

  • The chart file (Chart.yaml) is included to give both humans and tools an easy view into the contents of the chart.
  • The signature (SHA256, just like Docker) of the chart package (the .tgz file) is included, and may be used to verify the integrity of the chart package.
  • The entire body is signed using the algorithm used by PGP (see [http://keybase.io] for an emerging way of making crypto signing and verification easy).

The combination of this gives users the following assurances:

  • The package itself has not been tampered with (checksum package tgz).
  • The entity who released this package is known (via the GnuPG/PGP signature).

The format of the file looks something like this:

-----BEGIN PGP SIGNED MESSAGE-----
name: nginx
description: The nginx web server as a replication controller and service pair.
version: 0.5.1
keywords:
  - https
  - http
  - web server
  - proxy
source:
- https://github.com/foo/bar
home: http://nginx.com

...
files:
        nginx-0.5.1.tgz: “sha256:9f5270f50fc842cfcb717f817e95178f”
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.9 (GNU/Linux)

iEYEARECAAYFAkjilUEACgQkB01zfu119ZnHuQCdGCcg2YxF3XFscJLS4lzHlvte
WkQAmQGHuuoLEJuKhRNo+Wy7mhE7u1YG
=eifq
-----END PGP SIGNATURE-----

Note that the YAML section contains two documents (separated by ...\n). The first is the Chart.yaml. The second is the checksums, a map of filenames to SHA-256 digests (value shown is fake/truncated)

The signature block is a standard PGP signature, which provides tamper resistance.

Chart Repositories

Chart repositories serve as a centralized collection of Helm charts.

Chart repositories must make it possible to serve provenance files over HTTP via a specific request, and must make them available at the same URI path as the chart.

For example, if the base URL for a package is https://example.com/charts/mychart-1.2.3.tgz, the provenance file, if it exists, MUST be accessible at https://example.com/charts/mychart-1.2.3.tgz.prov.

From the end user’s perspective, helm install --verify myrepo/mychart-1.2.3 should result in the download of both the chart and the provenance file with no additional user configuration or action.

Establishing Authority and Authenticity

When dealing with chain-of-trust systems, it is important to be able to establish the authority of a signer. Or, to put this plainly, the system above hinges on the fact that you trust the person who signed the chart. That, in turn, means you need to trust the public key of the signer.

One of the design decisions with Kubernetes Helm has been that the Helm project would not insert itself into the chain of trust as a necessary party. We don’t want to be “the certificate authority” for all chart signers. Instead, we strongly favor a decentralized model, which is part of the reason we chose OpenPGP as our foundational technology. So when it comes to establishing authority, we have left this step more-or-less undefined in Helm 2.0.0.

However, we have some pointers and recommendations for those interested in using the provenance system:

  • The Keybase platform provides a public centralized repository for trust information.
    • You can use Keybase to store your keys or to get the public keys of others.
    • Keybase also has fabulous documentation available
    • While we haven’t tested it, Keybase’s “secure website” feature could be used to serve Helm charts.
  • The official Kubernetes Charts project is trying to solve this problem for the official chart repository.
    • There is a long issue there detailing the current thoughts.
    • The basic idea is that an official “chart reviewer” signs charts with her or his key, and the resulting provenance file is then uploaded to the chart repository.
    • There has been some work on the idea that a list of valid signing keys may be included in the index.yaml file of a repository.

Finally, chain-of-trust is an evolving feature of Helm, and some community members have proposed adapting part of the OSI model for signatures. This is an open line of inquiry in the Helm team. If you’re interested, jump on in.

+++ aliases = [ “chart_tests.md”, “docs/chart_tests.md”, “using_helm/chart_tests.md”, “developing_charts/chart_tests.md” ] +++

Chart Tests

A chart contains a number of Kubernetes resources and components that work together. As a chart author, you may want to write some tests that validate that your chart works as expected when it is installed. These tests also help the chart consumer understand what your chart is supposed to do.

A test in a helm chart lives under the templates/ directory and is a pod definition that specifies a container with a given command to run. The container should exit successfully (exit 0) for a test to be considered a success. The pod definition must contain one of the helm test hook annotations: helm.sh/hooks: test-success or helm.sh/hooks: test-failure.

Example tests: - Validate that your configuration from the values.yaml file was properly injected. - Make sure your username and password work correctly - Make sure an incorrect username and password does not work - Assert that your services are up and correctly load balancing - etc.

You can run the pre-defined tests in Helm on a release using the command helm test <RELEASE_NAME>. For a chart consumer, this is a great way to sanity check that their release of a chart (or application) works as expected.

A Breakdown of the Helm Test Hooks

In Helm, there are two test hooks: test-success and test-failure

test-success indicates that test pod should complete successfully. In other words, the containers in the pod should exit 0. test-failure is a way to assert that a test pod should not complete successfully. If the containers in the pod do not exit 0, that indicates success.

Example Test

Here is an example of a helm test pod definition in an example mariadb chart:

mariadb/
  Chart.yaml
  README.md
  values.yaml
  charts/
  templates/
  templates/tests/test-mariadb-connection.yaml

In wordpress/templates/tests/test-mariadb-connection.yaml:

apiVersion: v1
kind: Pod
metadata:
  name: "{{ .Release.Name }}-credentials-test"
  annotations:
    "helm.sh/hook": test-success
spec:
  containers:
  - name: {{ .Release.Name }}-credentials-test
    image: {{ .Values.image }}
    env:
      - name: MARIADB_HOST
        value: {{ template "mariadb.fullname" . }}
      - name: MARIADB_PORT
        value: "3306"
      - name: WORDPRESS_DATABASE_NAME
        value: {{ default "" .Values.mariadb.mariadbDatabase | quote }}
      - name: WORDPRESS_DATABASE_USER
        value: {{ default "" .Values.mariadb.mariadbUser | quote }}
      - name: WORDPRESS_DATABASE_PASSWORD
        valueFrom:
          secretKeyRef:
            name: {{ template "mariadb.fullname" . }}
            key: mariadb-password
    command: ["sh", "-c", "mysql --host=$MARIADB_HOST --port=$MARIADB_PORT --user=$WORDPRESS_DATABASE_USER --password=$WORDPRESS_DATABASE_PASSWORD"]
  restartPolicy: Never

Steps to Run a Test Suite on a Release

  1. $ helm install mariadb

    NAME:   quirky-walrus
    LAST DEPLOYED: Mon Feb 13 13:50:43 2017
    NAMESPACE: default
    STATUS: DEPLOYED
    
  2. $ helm test quirky-walrus

    RUNNING: quirky-walrus-credentials-test
    SUCCESS: quirky-walrus-credentials-test
    

Notes

  • You can define as many tests as you would like in a single yaml file or spread across several yaml files in the templates/ directory
  • You are welcome to nest your test suite under a tests/ directory like <chart-name>/templates/tests/ for more isolation

+++ aliases = [ “developing_charts_faq.md”, “docs/developing_charts_faq.md”, “using_helm/developing_charts_faq.md”, “developing_charts/developing_charts_faq.md” ] +++

Chart Repositories: Frequently Asked Questions

This section tracks some of the more frequently encountered issues with using chart repositories.

We’d love your help making this document better. To add, correct, or remove information, file an issue or send us a pull request.

Fetching

Q: Why do I get a unsupported protocol scheme "" error when trying to fetch a chart from my custom repo?

A: (Helm < 2.5.0) This is likely caused by you creating your chart repo index without specifying the --url flag. Try recreating your index.yaml file with a command like helm repo index --url http://my-repo/charts ., and then re-uploading it to your custom charts repo.

This behavior was changed in Helm 2.5.0.