Helm Concepts: Difference between revisions
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* [[Helm#Subjects|Helm]] | * [[Helm#Subjects|Helm]] | ||
* [[Helm Templates]] | * [[Helm Templates|Templates]] | ||
* [[Helm Dependencies]] | * [[Helm Configuration|Configuration]] | ||
* [[Helm Dependencies|Dependencies]] | |||
=Overview= | =Overview= | ||
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====Chart Name==== | ====Chart Name==== | ||
A chart is identified by its '''name''' in [[Helm_Repositories#Overview|repositories]]. Examples: "nginx" or "postgresql". The chart name is sometimes referred to as [[Helm_Repositories#Chart_Reference|chart reference]]. The name is part of the package identification, along with [[#Chart_Version|chart version]]. The name of the chart is also specified in the [[Helm_Chart_Chart.yaml#name|name]] field of the <code>Chart.yaml</code> metadata file. Chart names should use lower case letter and numbers, and start with a letter. Hyphens are allowed. Uppercase letter, underscores or dots should not be used in chart names. The directory that contains a chart must have the same name as the chart. For more details see [https://helm.sh/docs/chart_best_practices/#chart-names Chart Names Best Practices]. | A chart is identified by its '''name''' in [[Helm_Repositories#Overview|repositories]]. Examples: "nginx" or "postgresql". The chart name is sometimes referred to as [[Helm_Repositories#Chart_Reference|chart reference]]. The name is part of the package identification, along with [[#Chart_Version|chart version]]. The name of the chart is also specified in the <code>[[Helm_Chart_Chart.yaml#name|name]]</code> field of the <code>Chart.yaml</code> metadata file. Chart names should use lower case letter and numbers, and start with a letter. Hyphens are allowed. Uppercase letter, underscores or dots should not be used in chart names. | ||
The directory that contains a chart must have the same name as the chart. | |||
For more details see [https://helm.sh/docs/chart_best_practices/#chart-names Chart Names Best Practices]. | |||
====Chart Versioning==== | ====Chart Versioning==== | ||
<code>Chart.yaml</code> carries two version fields: the <span id='Chart_Version'></span>'''chart version''' (<code>[[Helm_Chart_Chart.yaml#version|version]]</code>) and the <span id='Application_Version'></span>'''application version''' (<code>[[Helm_Chart_Chart.yaml#appVersion|appVersion]]</code>). | |||
Every chart must have a [[Software_Development#Semantic_Versioning|SemVer 2]] version specified in the <code>version</code> field of the <code>Chart.yaml</code> metadata file. | |||
Every chart must have a [[Software_Development#Semantic_Versioning|SemVer 2]] version specified | |||
Packages exposed by [[#Repository|repositories]], as well as packages generated by [[helm package]] are identified by their [[#Chart_Name|name]] '''and''' their version. For example, the [[#Chart_Archive|chart archive]] of an "nginx" package whose version filed is "1.2.3" will be named: | Packages exposed by [[#Repository|repositories]], as well as packages generated by [[helm package]] are identified by their [[#Chart_Name|name]] '''and''' their version. For example, the [[#Chart_Archive|chart archive]] of an "nginx" package whose version filed is "1.2.3" will be named: | ||
<font size=-1> | |||
nginx-1.2.3.tgz | nginx-1.2.3.tgz | ||
</font> | |||
Helm tools rely on the version section of the chart archive file name as [[#Release_Marker|release marker]]. The system assumes that the version number in the chart package name matches the version number in the <code>Chart.yaml</code>. Failure to meet this assumption will cause an error. For more details on chart version see [https://helm.sh/docs/chart_best_practices/#version-numbers Chart Version Numbers Best Practices]. | |||
The <code>[[Helm_Chart_Chart.yaml#appVersion|appVersion]]</code> field is intended to carry an informal application version, not necessarily [[Software_Development#Semantic_Versioning|SemVer 2]], and independent from the <code>[[Helm_Chart_Chart.yaml#version|version]]</code> field. This field is informational, and has no impact on chart version calculations. It is very common for the chart version and app version to be different: | |||
The [[Helm_Chart_Chart.yaml#appVersion|appVersion]] field is intended to carry an informal application version, not necessarily [[Software_Development#Semantic_Versioning|SemVer 2]], and independent from the [[Helm_Chart_Chart.yaml#version|version]] field. This field is informational, and has no impact on chart version calculations. It is very common for the chart version and app version to be different: | |||
<syntaxhighlight lang='text'> | <syntaxhighlight lang='text'> | ||
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====Chart Archive==== | ====Chart Archive==== | ||
A chart archive is a chart in a packaged (tgz) format. The [[#Repository|chart repositories]] expose chart archives. [[helm package]] creates chart archives. | A chart archive is a chart in a packaged (tgz) format. The [[#Repository|chart repositories]] expose chart archives. The <code>[[helm package]]</code> command creates chart archives. | ||
====Chart Type==== | ====Chart Type==== | ||
The type designates a chart as 'application' or 'library'. 'application' is the default type. A 'library' or 'helper' chart provides utilities or functions for the chart builder, it has no resource object and therefore is not installable. Example: https://github.com/helm/charts/tree/master/incubator/common. | The type designates a chart as 'application' or 'library'. 'application' is the default type. A 'library' or 'helper' chart provides utilities or functions for the chart builder, it has no resource object and therefore is not installable. Example: https://github.com/helm/charts/tree/master/incubator/common. | ||
An application chart can be used as a library chart. This is enabled by setting the type to 'library'. The chart will then be rendered as a library chart where all utilities and functions can be leveraged. | An application chart can be used as a library chart. This is enabled by setting the type to 'library'. The chart will then be rendered as a library chart where all utilities and functions can be leveraged. No resource objects contained by the chart will be rendered. | ||
==Chart Installation== | ==Chart Installation== | ||
Charts are installed into a target Kubernetes cluster and turned into [[#Release|releases]] with: | Charts are installed into a target Kubernetes cluster and turned into [[#Release|releases]] with: | ||
<font size=-1> | |||
[[helm install]] | [[helm install]] | ||
The installation is an asynchronous process, the Helm client does not wait until all resources are running before it exits, this is because charts may | </font> | ||
The installation is an asynchronous process, the Helm client does not wait until all resources are running before it exits, this is because charts may need large container images that take long to install in the cluster. Without additional input, a chart will be installed with the [[Helm_Configuration#Default_Configuration|default configuration]], but [[Helm_Configuration#Overriding_Default_Configuration|custom configuration changes]] can be applied during the installation process. | |||
The default option for the helm install command is to install from the [[#Default_Repository|default repository]]. However, the chart may come from other sources: a [[Helm_repo#Add_a_New_Repository|different repository]], a [[Helm_install#Installing_from_a_File|local file]], an [[Helm_install#Installing_from_an_Unpacked_Chart_Directory|unpacked chart directory]] or a [[Helm_install#Installing_from_a_URL|URL]]. | The default option for the helm install command is to install from the [[Helm_Repositories#Default_Repository|default repository]]. However, the chart may come from other sources: a [[Helm_repo#Add_a_New_Repository|different repository]], a [[Helm_install#Installing_from_a_File|local file]], an [[Helm_install#Installing_from_an_Unpacked_Chart_Directory|unpacked chart directory]] or a [[Helm_install#Installing_from_a_URL|URL]]. | ||
===Resource Installation and De-Installation Order=== | ===Resource Installation and De-Installation Order=== | ||
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<font size=-1> | <font size=-1> | ||
archaeopteryx | archaeopteryx | ||
├─ <span id='Chart.yaml'></span>[[ | ├─ <span id='Chart.yaml'></span>[[Helm_Chart_Chart.yaml#Overview|Chart.yaml]] | ||
├─ <span id='values.yaml'></span>[[Helm Chart values.yaml|values.yaml]] | ├─ <span id='values.yaml'></span>[[Helm Chart values.yaml|values.yaml]] | ||
├─ <span id='LICENSE'></span>[[Helm Chart License|LICENSE]] | ├─ <span id='LICENSE'></span>[[Helm Chart License|LICENSE]] | ||
| Line 70: | Line 76: | ||
├─ [[#charts_Directory|charts]] | ├─ [[#charts_Directory|charts]] | ||
└─ [[Helm_Templates#The_templates.2F_Directory|templates]] | └─ [[Helm_Templates#The_templates.2F_Directory|templates]] | ||
├─ <span id='NOTES.txt'>[[Helm Chart NOTES.txt|NOTES.txt]] | ├─ <span id='NOTES.txt'></span>[[Helm Chart NOTES.txt|NOTES.txt]] | ||
├─ <span id='_helpers.tpl'></span>[[Helm Chart _helpers.tpl|_helpers.tpl]] | ├─ <span id='_helpers.tpl'></span>[[Helm Chart _helpers.tpl|_helpers.tpl]] | ||
├─ deployment.yaml | ├─ deployment.yaml | ||
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└─ tests | └─ tests | ||
</font> | </font> | ||
===<span id='charts_Directory'></span><tt>charts/</tt> Directory=== | |||
The 'charts' directory contains any charts upon which this chart depends. The content of the directory can either [[Helm Dependencies#Manual_Dependency|manually managed]], or it can be [[Helm Dependencies#Dynamic_Dependency|updated dynamically]] for dependencies declared in <code>[[Helm_Chart_Chart.yaml|Chart.yaml]]</code> for Helm 3 or <code>[[Helm_Chart_requirements.yaml|requirements.yaml]]</code> for Helm 2. A dependency can be either a [[#Chart_Archive|chart archive]] or an unpacked chart directory. If the name of the dependency, either file or directory, starts with '_' or '.', the dependency will be ignored by the chart loader. For more details on dependencies see: {{Internal|Helm_Dependencies#How_Helm_Dependencies_Work|How Helm Dependencies Work}} | |||
{{Internal|Helm_Templates#The_templates.2F_Directory|The templates/ Directory}} | ===<span id='templates_Directory'></span><tt>templates/</tt> Directory=== | ||
{{Internal|Helm_Templates#The_templates.2F_Directory|The <tt>templates/</tt> Directory}} | |||
==Developing Custom Charts== | ==Developing Custom Charts== | ||
The development of a custom chart could start with [[helm create]], which is a command that creates a standard chart directory layout along with some common files typically used in a chart. The command provides just a basic example and is not meant to cover all Kubernetes resources. While a chart is being developed, the syntactic consistency can be checked with [[helm lint]]. Then the chart is ready for delivery, it can be packaged with [[helm package]]. | The development of a custom chart could start with the <code>[[helm create]]</code> command, which is a command that creates a standard chart directory layout along with some common files typically used in a chart. The command provides just a basic example and is not meant to cover all Kubernetes resources. While a chart is being developed, the syntactic consistency can be checked with the <code>[[helm lint]]</code> command. Then the chart is ready for delivery, it can be packaged with <code>[[helm package]]</code>. | ||
==Chart Operations== | ==Chart Operations== | ||
* [[helm create]] | * <code>[[helm create]]</code> | ||
* [[helm lint]] | * <code>[[helm lint]]</code> | ||
* [[helm package]] | * <code>[[helm package]]</code> | ||
* [[helm install]] | * <code>[[helm install]]</code> | ||
* [[helm show]] | * <code>[[helm show]]</code> | ||
* [[Helm_get#Get_Manifest|helm get manifest]] | * <code>[[Helm_get#Get_Manifest|helm get manifest]]</code> | ||
=Release= | =Release= | ||
A release is a running instance of a [[#Chart|chart]], to which a specific [[Helm_Configuration#Overview|configuration]] was applied. Whenever a chart is installed, a new release is created. One chart can be installed multiple times into the same cluster, and each can be independently managed and upgraded. Each release has its own [[#Release_Name|release name]]. It is important to know that releases are namespace-scoped. There could be two releases with the same name, but in two different namespaces. | |||
When a new version of a chart is released, or when the configuration of a release changes, the release can be upgraded with the <code>[[helm upgrade]]</code> command. Helm tries to perform the least invasive upgrade, and only upgraded things that changed since the last release. If something fails during the upgrade, a rollback can be performed with the <code>[[helm rollback]]</code> command. | |||
When a new version of a chart is released, or when the configuration of a release | |||
At a certain moment in time, a release is in a certain [[#Release_State|state]]. | At a certain moment in time, a release is in a certain [[#Release_State|state]]. | ||
Releases can be uninstalled with [[helm uninstall]]. Helm keeps a history of deleted releases, which can be retrieved with [[Helm_list#Show_Deleted_Releases|helm list --deleted]]. | Releases can be uninstalled with the <code>[[helm uninstall]]</code>. Helm keeps a history of deleted releases, which can be retrieved with the <code>[[Helm_list#Show_Deleted_Releases|helm list --deleted]]</code>. | ||
==Release Name== | ==Release Name== | ||
If not specified, release names are generated (e.g. "happy-panda"). To specify a release name, use [[Helm_install#Specifying_a_Release_Name|helm install | If not specified, release names are generated (e.g. "happy-panda"). To specify a release name, use the <code>[[Helm_install#Specifying_a_Release_Name|helm install <name> ...]]</code> command. Helm keeps records of deleted releases, so a release name first used by a deleted release cannot be re-used (unless <code>--replace</code> is used). The release name is available in templates as a built-in object: | ||
<font size=-1> | |||
{{ [[Helm_Templates#Release.Name|.Release.Name]] }} | {{ [[Helm_Templates#Release.Name|.Release.Name]] }} | ||
</font> | |||
Many charts are configured so Kubernetes resources created during a Helm installation carry a "release" [[#Labels|label]] with the value set to the release name. | Many charts are configured so Kubernetes resources created during a Helm installation carry a "release" [[#Labels|label]] with the value set to the release name. | ||
==Release Revision== | ==Release Revision== | ||
A release version (revision) is incremental. Every time an install, upgrade or rollback happens, the revision number is incremented by 1, and the first revision is always 1. The revision numbers for a certain release can be inspected with [[helm history]]. A release revision can be used during a [[helm rollback|rollback]]. The release revision is available in templates as a built-in object: | A release version (revision) is incremental. Every time an install, upgrade or rollback happens, the revision number is incremented by 1, and the first revision is always 1. The revision numbers for a certain release can be inspected with the <code>[[helm history]]</code> command. A release revision can be used during a [[helm rollback|rollback]]. The release revision is available in templates as a built-in object: | ||
<font size=-1> | |||
{{ [[Helm_Templates#Release.Revision|.Release.Revision]] }} | {{ [[Helm_Templates#Release.Revision|.Release.Revision]] }} | ||
</font> | |||
==Release State== | ==Release State== | ||
The release state is reported by [[Helm_status|helm status]]. | The release state is reported by the <code>[[Helm_status|helm status]]</code> command. | ||
A release state is one of: | A release state is one of: | ||
===unknown=== | ===<tt>unknown</tt>=== | ||
===deployed=== | ===<tt>deployed</tt>=== | ||
===uninstalled=== | ===<tt>uninstalled</tt>=== | ||
===superseded=== | ===<tt>superseded</tt>=== | ||
===failed=== | ===<tt>failed</tt>=== | ||
===uninstalling=== | ===<tt>uninstalling</tt>=== | ||
===pending-install=== | ===<tt>pending-install</tt>=== | ||
===pending-upgrade=== | ===<tt>pending-upgrade</tt>=== | ||
===pending-rollback=== | ===<tt>pending-rollback</tt>=== | ||
==Release Marker== | ==Release Marker== | ||
| Line 173: | Line 167: | ||
Normally, all resources created by a Helm installation are removed upon uninstallation: Helm uninstalls by default all resources created by the chart for the release being uninstalled. There are cases when we may want to keep resources around: one case is when we want to keep a PersistentVolumeClaim because deleting it would make the a PersistentVolume outside of our control unavailable for binding for the subsequent release. | Normally, all resources created by a Helm installation are removed upon uninstallation: Helm uninstalls by default all resources created by the chart for the release being uninstalled. There are cases when we may want to keep resources around: one case is when we want to keep a PersistentVolumeClaim because deleting it would make the a PersistentVolume outside of our control unavailable for binding for the subsequent release. | ||
To indicate to Helm that a resource should be kept on uninstall, use the "helm.sh/resource-policy" annotation in template: | To indicate to Helm that a resource should be kept on uninstall, use the <code>"helm.sh/resource-policy"</code> annotation in template: | ||
<syntaxhighlight lang='yaml'> | <syntaxhighlight lang='yaml'> | ||
| Line 182: | Line 176: | ||
</syntaxhighlight> | </syntaxhighlight> | ||
The "helm.sh/resource-policy" instructs helm to skip deleting the resource on uninstall, [[Helm upgrade|upgrade]] or [[Helm rollback|rollback]] operations. | The <code>"helm.sh/resource-policy"</code> instructs helm to skip deleting the resource on uninstall, [[Helm upgrade|upgrade]] or [[Helm rollback|rollback]] operations. | ||
Note that this resource becomes orphaned, it will be no longer be managed by Helm. This can lead to problems | Note that this resource becomes orphaned, it will be no longer be managed by Helm. This can lead to problems when using the <code>[[Helm_install#--replace|helm install --replace]]</code> command on a release that has already been uninstalled, but has kept resources. | ||
<font color=darkgray>Helm does not seem to remove the [[Helm_Concepts#Resource_Association_with_a_Release|annotations and labels it placed on the resource]], so how does it know not to manage it anymore?</font> | <font color=darkgray>Helm does not seem to remove the [[Helm_Concepts#Resource_Association_with_a_Release|annotations and labels it placed on the resource]], so how does it know not to manage it anymore?</font> | ||
==Release Operations== | ==Release Operations== | ||
* [[helm install]] | * <code>[[helm install]]</code> | ||
* [[Helm_get#Get_Manifest|helm get manifest]] - display the manifest content that was posted to the server as part of the installation process. | * <code>[[Helm_get#Get_Manifest|helm get manifest]]</code> - display the manifest content that was posted to the server as part of the installation process. | ||
* [[helm list]] - display currently deployed releases. | * <code>[[helm list]]</code> - display currently deployed releases. | ||
* [[helm history]] | * <code>[[helm history]]</code> | ||
* [[helm status]] | * <code>[[helm status]]</code> | ||
* [[helm upgrade]] | * <code>[[helm upgrade]]</code> | ||
* [[helm rollback]] | * <code>[[helm rollback]]</code> | ||
* [[helm uninstall]] | * <code>[[helm uninstall]]</code> | ||
=<span id='Runtime'></span>The Helm Client= | |||
The Helm client is a command-line client for end users. The client is responsible for managing [[#Chart|charts]]. It helps with [[#Developing_Custom_Charts|local chart development]] and manages the interaction with [[#Repository|chart repositories]]. The interaction with the server consists in installing charts and providing a CLI for the [[#Release|release]] life cycle (the server manages the releases). | |||
=<span id='Template'></span>Templates= | |||
{{Internal|Helm Templates|Helm Templates}} | |||
= | =Configuration= | ||
{{Internal|Helm Configuration|Configuration}} | |||
== | =<span id='Dependency'></span><span id='Dynamic_Dependencies'></span><span id='Dependency_Selective_Loading'></span><span id='Importing_Child_Values'></span><span id='Manual_Dependencies'></span><span id='Subcharts'></span><span id='Dependency_Operations'></span><span id='Dynamic_.28requirements.yaml.29_Dependencies'></span>Dependencies= | ||
{{Internal|Helm Dependencies|Helm Dependencies}} | |||
=<span id='Repository_Name'></span><span id='Repository_URL'></span><span id='Default_Repository'></span><span id='Local_Cache'></span><span id='Chart_Reference'></span><span id='Repository_Operations'></span>Repository= | |||
{{Internal|Helm Repositories|Helm Repository}} | |||
== | |||
=Hooks= | =Hooks= | ||
| Line 232: | Line 223: | ||
Most charts configure the Kubernetes resources created by them to carry a "release" label, whose value is the [[#Release_Name|release name]]. This convention could be useful in providing a mechanism to identify these resources using [[Kubernetes Selector Concepts|label selectors]]. | Most charts configure the Kubernetes resources created by them to carry a "release" label, whose value is the [[#Release_Name|release name]]. This convention could be useful in providing a mechanism to identify these resources using [[Kubernetes Selector Concepts|label selectors]]. | ||
=Deprecated Elements= | =<span id='Deprecated_Elements'></span>Helm 2 Deprecated Elements= | ||
* <code>[[Helm Chart requirements.yaml|requirements.yaml]]</code> | * <code>[[Helm Chart requirements.yaml|requirements.yaml]]</code> | ||
* <code>[[Helm Chart requirements.lock|requirements.lock]]</code> | * <code>[[Helm Chart requirements.lock|requirements.lock]]</code> | ||
* [[Helm Tiller|Tiller]] | |||
Latest revision as of 00:23, 6 February 2022
Internal
Overview
Helm is a tool for managing Kubernetes packages called charts. Helm creates new charts from scratch, packages charts into chart archives (tgz) files, interacts with chart repositories where charts are stored, and finally installs and manages the release cycle of the underlying applications into an existing Kubernetes cluster. The installation process takes a chart, applies custom, operational environment-specific configuration and installs the chart into the Kubernetes cluster, creating a release.
Helm allows defining an application as a set of Kubernetes cluster components and provides mechanisms to manage these sets for their entire lifecycle.
Chart
A chart is a Helm package and a package format, the Kubernetes equivalent of a yum RPM file or a Homebrew formula. A chart contains all resource definitions necessary to deploy and run an application inside Kubernetes, arranged in a specific layout. A chart may be used to deploy a simple application, or a full web application stack with multiple dependencies, such as HTTP servers, database, caches and so on. A chart can be unpackaged, in which case it is a folder with files that follow the Helm chart rules and conventions. A chart can also be packaged, as a tar.gz chart archive.
Chart Name
A chart is identified by its name in repositories. Examples: "nginx" or "postgresql". The chart name is sometimes referred to as chart reference. The name is part of the package identification, along with chart version. The name of the chart is also specified in the name field of the Chart.yaml metadata file. Chart names should use lower case letter and numbers, and start with a letter. Hyphens are allowed. Uppercase letter, underscores or dots should not be used in chart names.
The directory that contains a chart must have the same name as the chart.
For more details see Chart Names Best Practices.
Chart Versioning
Chart.yaml carries two version fields: the chart version (version) and the application version (appVersion).
Every chart must have a SemVer 2 version specified in the version field of the Chart.yaml metadata file.
Packages exposed by repositories, as well as packages generated by helm package are identified by their name and their version. For example, the chart archive of an "nginx" package whose version filed is "1.2.3" will be named:
nginx-1.2.3.tgz
Helm tools rely on the version section of the chart archive file name as release marker. 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. For more details on chart version see Chart Version Numbers Best Practices.
The appVersion field is intended to carry an informal application version, not necessarily SemVer 2, and independent from the version field. This field is informational, and has no impact on chart version calculations. It is very common for the chart version and app version to be different:
NAME CHART VERSION APP VERSION DESCRIPTION
stable/postgresql 6.3.2 11.5.0 Chart for PostgreSQL, an object-relational database manag...
Chart Archive
A chart archive is a chart in a packaged (tgz) format. The chart repositories expose chart archives. The helm package command creates chart archives.
Chart Type
The type designates a chart as 'application' or 'library'. 'application' is the default type. A 'library' or 'helper' chart provides utilities or functions for the chart builder, it has no resource object and therefore is not installable. Example: https://github.com/helm/charts/tree/master/incubator/common. An application chart can be used as a library chart. This is enabled by setting the type to 'library'. The chart will then be rendered as a library chart where all utilities and functions can be leveraged. No resource objects contained by the chart will be rendered.
Chart Installation
Charts are installed into a target Kubernetes cluster and turned into releases with:
helm install
The installation is an asynchronous process, the Helm client does not wait until all resources are running before it exits, this is because charts may need large container images that take long to install in the cluster. Without additional input, a chart will be installed with the default configuration, but custom configuration changes can be applied during the installation process.
The default option for the helm install command is to install from the default repository. However, the chart may come from other sources: a different repository, a local file, an unpacked chart directory or a URL.
Resource Installation and De-Installation Order
Chart Layout
This section describes a typical chart directory tree. The top level directory is the chart name, without the version information.
archaeopteryx ├─ Chart.yaml ├─ values.yaml ├─ LICENSE ├─ README.md ├─ .helmignore ├─ charts └─ templates ├─ NOTES.txt ├─ _helpers.tpl ├─ deployment.yaml ├─ service.yaml │ ... └─ tests
charts/ Directory
The 'charts' directory contains any charts upon which this chart depends. The content of the directory can either manually managed, or it can be updated dynamically for dependencies declared in Chart.yaml for Helm 3 or requirements.yaml for Helm 2. A dependency can be either a chart archive or an unpacked chart directory. If the name of the dependency, either file or directory, starts with '_' or '.', the dependency will be ignored by the chart loader. For more details on dependencies see:
templates/ Directory
Developing Custom Charts
The development of a custom chart could start with the helm create command, which is a command that creates a standard chart directory layout along with some common files typically used in a chart. The command provides just a basic example and is not meant to cover all Kubernetes resources. While a chart is being developed, the syntactic consistency can be checked with the helm lint command. Then the chart is ready for delivery, it can be packaged with helm package.
Chart Operations
Release
A release is a running instance of a chart, to which a specific configuration was applied. Whenever a chart is installed, a new release is created. One chart can be installed multiple times into the same cluster, and each can be independently managed and upgraded. Each release has its own release name. It is important to know that releases are namespace-scoped. There could be two releases with the same name, but in two different namespaces.
When a new version of a chart is released, or when the configuration of a release changes, the release can be upgraded with the helm upgrade command. Helm tries to perform the least invasive upgrade, and only upgraded things that changed since the last release. If something fails during the upgrade, a rollback can be performed with the helm rollback command.
At a certain moment in time, a release is in a certain state.
Releases can be uninstalled with the helm uninstall. Helm keeps a history of deleted releases, which can be retrieved with the helm list --deleted.
Release Name
If not specified, release names are generated (e.g. "happy-panda"). To specify a release name, use the helm install <name> ... command. Helm keeps records of deleted releases, so a release name first used by a deleted release cannot be re-used (unless --replace is used). The release name is available in templates as a built-in object:
{{ .Release.Name }}
Many charts are configured so Kubernetes resources created during a Helm installation carry a "release" label with the value set to the release name.
Release Revision
A release version (revision) is incremental. Every time an install, upgrade or rollback happens, the revision number is incremented by 1, and the first revision is always 1. The revision numbers for a certain release can be inspected with the helm history command. A release revision can be used during a rollback. The release revision is available in templates as a built-in object:
{{ .Release.Revision }}
Release State
The release state is reported by the helm status command.
A release state is one of:
unknown
deployed
uninstalled
superseded
failed
uninstalling
pending-install
pending-upgrade
pending-rollback
Release Marker
The package version is included in the release marker.
Release Lifecycle
Resource Association with a Release
Resources created by Helm are associated with their Helm release via annotations:
kind: ...
metadata:
annotations:
meta.helm.sh/release-name: release-example
meta.helm.sh/release-namespace: namespace-example
labels:
app.kubernetes.io/managed-by: Helm
Preventing Resource Deletion upon Uninstallation
Normally, all resources created by a Helm installation are removed upon uninstallation: Helm uninstalls by default all resources created by the chart for the release being uninstalled. There are cases when we may want to keep resources around: one case is when we want to keep a PersistentVolumeClaim because deleting it would make the a PersistentVolume outside of our control unavailable for binding for the subsequent release.
To indicate to Helm that a resource should be kept on uninstall, use the "helm.sh/resource-policy" annotation in template:
kind: Something
metadata:
annotations:
helm.sh/resource-policy: keep
The "helm.sh/resource-policy" instructs helm to skip deleting the resource on uninstall, upgrade or rollback operations.
Note that this resource becomes orphaned, it will be no longer be managed by Helm. This can lead to problems when using the helm install --replace command on a release that has already been uninstalled, but has kept resources.
Helm does not seem to remove the annotations and labels it placed on the resource, so how does it know not to manage it anymore?
Release Operations
helm installhelm get manifest- display the manifest content that was posted to the server as part of the installation process.helm list- display currently deployed releases.helm historyhelm statushelm upgradehelm rollbackhelm uninstall
The Helm Client
The Helm client is a command-line client for end users. The client is responsible for managing charts. It helps with local chart development and manages the interaction with chart repositories. The interaction with the server consists in installing charts and providing a CLI for the release life cycle (the server manages the releases).
Templates
Configuration
Dependencies
Repository
Hooks
Security
Plugins
Tests
Labels
Most charts configure the Kubernetes resources created by them to carry a "release" label, whose value is the release name. This convention could be useful in providing a mechanism to identify these resources using label selectors.