Changes Since Helm 2

Changes since Helm 2

Here’s an exhaustive list of all the major changes introduced in Helm 3.

Removal of Tiller

During the Helm 2 development cycle, we introduced Tiller. Tiller played an important role for teams working on a shared cluster - it made it possible for multiple different operators to interact with the same set of releases.

With role-based access controls (RBAC) enabled by default in Kubernetes 1.6, locking down Tiller for use in a production scenario became more difficult to manage. Due to the vast number of possible security policies, our stance was to provide a permissive default configuration. This allowed first-time users to start experimenting with Helm and Kubernetes without having to dive headfirst into the security controls. Unfortunately, this permissive configuration could grant a user a broad range of permissions they weren’t intended to have. DevOps and SREs had to learn additional operational steps when installing Tiller into a multi-tenant cluster.

After hearing how community members were using Helm in certain scenarios, we found that Tiller’s release management system did not need to rely upon an in-cluster operator to maintain state or act as a central hub for Helm release information. Instead, we could simply fetch information from the Kubernetes API server, render the Charts client-side, and store a record of the installation in Kubernetes.

Tiller’s primary goal could be accomplished without Tiller, so one of the first decisions we made regarding Helm 3 was to completely remove Tiller.

With Tiller gone, the security model for Helm is radically simplified. Helm 3 now supports all the modern security, identity, and authorization features of modern Kubernetes. Helm’s permissions are evaluated using your kubeconfig file. Cluster administrators can restrict user permissions at whatever granularity they see fit. Releases are still recorded in-cluster, and the rest of Helm’s functionality remains.

Improved Upgrade Strategy: 3-way Strategic Merge Patches

Helm 2 used a two-way strategic merge patch. During an upgrade, it compared the most recent chart’s manifest against the proposed chart’s manifest (the one supplied during helm upgrade). It compared the differences between these two charts to determine what changes needed to be applied to the resources in Kubernetes. If changes were applied to the cluster out-of-band (such as during a kubectl edit), those changes were not considered. This resulted in resources being unable to roll back to its previous state: because Helm only considered the last applied chart’s manifest as its current state, if there were no changes in the chart’s state, the live state was left unchanged.

In Helm 3, we now use a three-way strategic merge patch. Helm considers the old manifest, its live state, and the new manifest when generating a patch.

Examples

Let’s go through a few common examples what this change impacts.

Rolling back where live state has changed

Your team just deployed their application to production on Kubernetes using Helm. The chart contains a Deployment object where the number of replicas is set to three:

$ helm install myapp ./myapp

A new developer joins the team. On their first day while observing the production cluster, a horrible coffee-spilling-on-the-keyboard accident happens and they kubectl scale the production deployment from three replicas down to zero.

$ kubectl scale --replicas=0 deployment/myapp

Another developer on your team notices that the production site is down and decides to rollback the release to its previous state:

$ helm rollback myapp

What happens?

In Helm 2, it would generate a patch, comparing the old manifest against the new manifest. Because this is a rollback, it’s the same manifest. Helm would determine that there is nothing to change because there is no difference between the old manifest and the new manifest. The replica count continues to stay at zero. Panic ensues.

In Helm 3, the patch is generated using the old manifest, the live state, and the new manifest. Helm recognizes that the old state was at three, the live state is at zero and the new manifest wishes to change it back to three, so it generates a patch to change the state back to three.

Upgrades where live state has changed

Many service meshes and other controller-based applications inject data into Kubernetes objects. This can be something like a sidecar, labels, or other information. Previously if you had the given manifest rendered from a Chart:

containers:
- name: server
  image: nginx:2.0.0

And the live state was modified by another application to

containers:
- name: server
  image: nginx:2.0.0
- name: my-injected-sidecar
  image: my-cool-mesh:1.0.0

Now, you want to upgrade the nginx image tag to 2.1.0. So, you upgrade to a chart with the given manifest:

containers:
- name: server
  image: nginx:2.1.0

What happens?

In Helm 2, Helm generates a patch of the containers object between the old manifest and the new manifest. The cluster’s live state is not considered during the patch generation.

The cluster’s live state is modified to look like the following:

containers:
- name: server
  image: nginx:2.1.0

The sidecar pod is removed from live state. More panic ensues.

In Helm 3, Helm generates a patch of the containers object between the old manifest, the live state, and the new manifest. It notices that the new manifest changes the image tag to 2.1.0, but live state contains a sidecar container.

The cluster’s live state is modified to look like the following:

containers:
- name: server
  image: nginx:2.1.0
- name: my-injected-sidecar
  image: my-cool-mesh:1.0.0

Release Names are now scoped to the Namespace

With the removal of Tiller, the information about each release had to go somewhere. In Helm 2, this was stored in the same namespace as Tiller. In practice, this meant that once a name was used by a release, no other release could use that same name, even if it was deployed in a different namespace.

In Helm 3, information about a particular release is now stored in the same namespace as the release itself. This means that users can now helm install wordpress stable/wordpress in two separate namespaces, and each can be referred with helm list by changing the current namespace context (e.g. helm list --namespace foo).

With this greater alignment to native cluster namespaces, the helm list command no longer lists all releases by default. Instead, it will list only the releases in the namespace of your current kubernetes context (i.e. the namespace shown when you run kubectl config view --minify). It also means you must supply the --all-namespaces flag to helm list to get behaviour similar to Helm 2.

Secrets as the default storage driver

In Helm 3, Secrets are now used as the default storage driver. Helm 2 used ConfigMaps by default to store release information. In Helm 2.7.0, a new storage backend that uses Secrets for storing release information was implemented, and it is now the default starting in Helm 3.

Changing to Secrets as the Helm 3 default allows for additional security in protecting charts in conjunction with the release of Secret encryption in Kubernetes.

Encrypting secrets at rest became available as an alpha feature in Kubernetes 1.7 and became stable as of Kubernetes 1.13. This allows users to encrypt Helm release metadata at rest, and so it is a good starting point that can be expanded later into using something like Vault.

Go import path changes

In Helm 3, Helm switched the Go import path over from k8s.io/helm to helm.sh/helm/v3. If you intend to upgrade to the Helm 3 Go client libraries, make sure to change your import paths.

Capabilities

The .Capabilities built-in object available during the rendering stage has been simplified.

Built-in Objects

Validating Chart Values with JSONSchema

A JSON Schema can now be imposed upon chart values. This ensures that values provided by the user follow the schema laid out by the chart maintainer, providing better error reporting when the user provides an incorrect set of values for a chart.

Validation occurs when any of the following commands are invoked:

• helm install
• helm upgrade
• helm template
• helm lint

See the documentation on Schema files for more information.

Consolidation of requirements.yaml into Chart.yaml

The Chart dependency management system moved from requirements.yaml and requirements.lock to Chart.yaml and Chart.lock. We recommend that new charts meant for Helm 3 use the new format. However, Helm 3 still understands Chart API version 1 (v1) and will load existing requirements.yaml files

In Helm 2, this is how a requirements.yaml looked:

dependencies:
- name: mariadb
  version: 5.x.x
  repository: https://charts.helm.sh/stable
  condition: mariadb.enabled
  tags:
    - database

In Helm 3, the dependency is expressed the same way, but now from your Chart.yaml:

dependencies:
- name: mariadb
  version: 5.x.x
  repository: https://charts.helm.sh/stable
  condition: mariadb.enabled
  tags:
    - database

Charts are still downloaded and placed in the charts/ directory, so subcharts vendored into the charts/ directory will continue to work without modification.

Name (or —generate-name) is now required on install

In Helm 2, if no name was provided, an auto-generated name would be given. In production, this proved to be more of a nuisance than a helpful feature. In Helm 3, Helm will throw an error if no name is provided with helm install.

For those who still wish to have a name auto-generated for you, you can use the --generate-name flag to create one for you.

Pushing Charts to OCI Registries

This is an experimental feature introduced in Helm 3. To use, set the environment variable HELM_EXPERIMENTAL_OCI=1.

At a high level, a Chart Repository is a location where Charts can be stored and shared. The Helm client packs and ships Helm Charts to a Chart Repository. Simply put, a Chart Repository is a basic HTTP server that houses an index.yaml file and some packaged charts.

While there are several benefits to the Chart Repository API meeting the most basic storage requirements, a few drawbacks have started to show:

• Chart Repositories have a very hard time abstracting most of the security implementations required in a production environment. Having a standard API for authentication and authorization is very important in production scenarios.
• Helm’s Chart provenance tools used for signing and verifying the integrity and origin of a chart are an optional piece of the Chart publishing process.
• In multi-tenant scenarios, the same Chart can be uploaded by another tenant, costing twice the storage cost to store the same content. Smarter chart repositories have been designed to handle this, but it’s not a part of the formal specification.
• Using a single index file for search, metadata information, and fetching Charts has made it difficult or clunky to design around in secure multi-tenant implementations.

Docker’s Distribution project (also known as Docker Registry v2) is the successor to the Docker Registry project. Many major cloud vendors have a product offering of the Distribution project, and with so many vendors offering the same product, the Distribution project has benefited from many years of hardening, security best practices, and battle-testing.

Please have a look at helm help chart and helm help registry for more information on how to package a chart and push it to a Docker registry.

For more info, please see this page.

Removal of helm serve

helm serve ran a local Chart Repository on your machine for development purposes. However, it didn’t receive much uptake as a development tool and had numerous issues with its design. In the end, we decided to remove it and split it out as a plugin.

For a similar experience to helm serve, have a look at the local filesystem storage option in ChartMuseum and the servecm plugin.

Library chart support

Helm 3 supports a class of chart called a “library chart”. This is a chart that is shared by other charts, but does not create any release artifacts of its own. A library chart’s templates can only declare define elements. Globally scoped non-define content is simply ignored. This allows users to re-use and share snippets of code that can be re-used across many charts, avoiding redundancy and keeping charts DRY.

Library charts are declared in the dependencies directive in Chart.yaml, and are installed and managed like any other chart.

dependencies:
  - name: mylib
    version: 1.x.x
    repository: quay.io

We’re very excited to see the use cases this feature opens up for chart developers, as well as any best practices that arise from consuming library charts.

Chart.yaml apiVersion bump

With the introduction of library chart support and the consolidation of requirements.yaml into Chart.yaml, clients that understood Helm 2’s package format won’t understand these new features. So, we bumped the apiVersion in Chart.yaml from v1 to v2.

helm create now creates charts using this new format, so the default apiVersion was bumped there as well.

Clients wishing to support both versions of Helm charts should inspect the apiVersion field in Chart.yaml to understand how to parse the package format.

XDG Base Directory Support

The XDG Base Directory Specification is a portable standard defining where configuration, data, and cached files should be stored on the filesystem.

In Helm 2, Helm stored all this information in ~/.helm (affectionately known as helm home), which could be changed by setting the $HELM_HOME environment variable, or by using the global flag --home.

In Helm 3, Helm now respects the following environment variables as per the XDG Base Directory Specification:

• $XDG_CACHE_HOME
• $XDG_CONFIG_HOME
• $XDG_DATA_HOME

Helm plugins are still passed $HELM_HOME as an alias to $XDG_DATA_HOME for backwards compatibility with plugins looking to use $HELM_HOME as a scratchpad environment.

Several new environment variables are also passed in to the plugin’s environment to accommodate this change:

• $HELM_PATH_CACHE for the cache path
• $HELM_PATH_CONFIG for the config path
• $HELM_PATH_DATA for the data path

Helm plugins looking to support Helm 3 should consider using these new environment variables instead.

CLI Command Renames

In order to better align the verbiage from other package managers, helm delete was re-named to helm uninstall. helm delete is still retained as an alias to helm uninstall, so either form can be used.

In Helm 2, in order to purge the release ledger, the --purge flag had to be provided. This functionality is now enabled by default. To retain the previous behavior, use helm uninstall --keep-history.

Additionally, several other commands were re-named to accommodate the same conventions:

• helm inspect -> helm show
• helm fetch -> helm pull

These commands have also retained their older verbs as aliases, so you can continue to use them in either form.

Automatically creating namespaces

When creating a release in a namespace that does not exist, Helm 2 created the namespace. Helm 3 follows the behavior of other Kubernetes tooling and returns an error if the namespace does not exist. Helm 3 will create the namespace if you explicitly specify --create-namespace flag.

What happened to .Chart.ApiVersion?

Helm follows the typical convention for CamelCasing which is to capitalize an acronym. We have done this elsewhere in the code, such as with .Capabilities.APIVersions.Has. In Helm v3, we corrected .Chart.ApiVersion to follow this pattern, renaming it to .Chart.APIVersion.

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