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Chart sources

In the introduction we created a simple HelmRelease that made use of a chart from a Helm repository, but the Helm Operator does support multiple chart sources, and virtually any protocol and/or source that can be shelled-in through a Helm downloader plugin.

In this section of the guide we will take a deeper dive into the available chart sources, and the unique features they have.

Comparison

The following are short lists of the major characteristics of the different chart sources. Keep these in mind when you have to make a decision about what type of chart source to use for your HelmRelease, as they result in quite different behaviour.

Charts from Helm repositories

  • Are immutable and non-moving (i.e. no updates for the chart itself are received unless the .chart.version is changed).
  • Are cached for the lifetime duration of the Helm Operator pod.
  • Are shared between HelmRelease resources making use of the same chart and version.
  • Require a custom repositories.yaml to be mounted and imported when authentication is required.
  • Are not just limited to HTTP/S.
  • Do not support chart dependency updates (but instead use the dependencies bundled with the chart).
  • Do not support valuesFrom.chartFileRef.

Charts from Git repositories

  • Move by mirroring the Git repository and fetching the latest HEAD for the configured .chart.ref on an interval (i.e. when a change is detected in Git under the .chart.path, a release will be scheduled for an upgrade).
  • Share their Git repository mirror with HelmRelease resources making use of the same .chart.git, .chart.ref and .chart.secretKeyRef.
  • Require a private key to be mounted for Git over SSH.
  • Support credentials from a secret or a global .netrc file for Git over HTTPS.
  • Do support chart dependency updates
  • Do support valuesFrom.chartFileRef to make use of alternative value files present in the .chart.path.

Helm repositories

The Helm repository chart source is defined as follows in the .spec of a HelmRelease. All listed fields are mandatory:

spec:
  chart:
    repository: https://stefanprodan.github.io/podinfo
    name: podinfo
    version: 3.2.0

The definition of the listed keys is as follows:

  • repository: The URL of the Helm repository, e.g. https://kubernetes-charts.storage.googleapis.com or https://charts.example.com.

Putting /index.yaml behind the URL it should return an index file with all available charts for the Helm repository. * name: The name of the Helm chart without an alias, e.g. podinfo (instead of <alias>/podinfo).

Having doubts about what to put here? Use the name as listed in the Chart.yaml of the Helm chart you want to use. * version: The targeted Helm chart version, e.g. 3.2.0.

In the introduction you already had a brief exposure to this chart source, and in essence Helm repositories are the simplest way to make use of a Helm chart in a HelmRelease.

To be able to perform releases with them the Helm Operator only makes use of native Helm features and a tiny bit of glue to wire things together:

It will first attempt a reverse lookup for a repository alias in the local repositories.yaml for the defined repository URL, if an alias is found it will use this alias with the given name and version to instruct Helm to fetch the chart to a cache path defined by the Helm Operator.

If the reverse lookup failed and no alias was found for the given URL it will fallback to attempting to retrieve the absolute URL of the chart from the index of the given repository URL, this URL is then used to instruct Helm to fetch the chart to a cache path defined by the Helm Operator.

When this does not succeed either a status condition of type ChartFetched will be recorded on the HelmRelease resource with the returned error.

Authentication and certificates

Some Helm repositories require authentication or certificates before you are able to make use of any charts they hold. At present, per-resource authentication is not implemented for Helm repositories. The HelmRelease Custom Resource does include a field chartPullSecret for attaching a repositories.yaml file, but this has not been actually implemented.

As a workaround, you can mount a repositories.yaml file with authentication already configured (and any required certificates) into the Helm Operator container, and import it using the --helm-repository-import flag.

First, create a new empty repositories.yaml file locally:

touch repositories.yaml

You can now use helm to write the repository entry to this new file. Using Helm 3 for this is the best option as it offers a --repository-config flag and the generated output works for both versions:

helm repo add \
    --repository-config $PWD/repositories.yaml \
    --username <username> \
    --password <password> \
    <alias> <URL>

Note

For Azure ACR repositories, you will need to create a service principal and use the plain text ID and password this gives you.

If you need to define any certificates, edit the respective caFile, certFile and keyFile values of the entry you just added to the mount paths you will later add to the Helm Operator container (example path used here is /var/certs/*):

- caFile: /var/certs/ca.crt
  certFile: /var/certs/cert.crt
  keyFile: /var/certs/auth.key
  name: <alias>

Now you can create a secret in the same namespace as you are running the Helm operator, from the repositories file:

kubectl create secret generic flux-helm-repositories \
    --from-file=$PWD/repositories.yaml

In case you defined any certificate entries, also create a secret for those files in the same namespace as you are running the Helm Operator:

kubectl create secret generic flux-helm-repository-certs \
    --from-file=$PWD/ca.crt \
    --from-file=$PWD/cert.crt \
    --from-file=$PWD/auth.key

Mount the created secret(s) by adding to volumes in the pod spec of the Helm operator deployment, and volumeMounts of the Helm Operator container. A good mount path for the repositories.yaml file that does not give conflicts with any Helm paths is /root/.helm/repository/repositories.yaml. Examples of this can be found in the commented-out sections of the example deployment.

Lastly, configure the --helm-repository-import argument on the Helm Operator container for your enabled Helm versions:

        args:
        - --helm-repository-import=v2:/root/.helm/repository/repositories.yaml,v3:/root/.helm/repository/repositories.yaml

Note

There is no limit to the amount of repository files that can be imported as the --helm-repository-import flag accepts a comma separated string slice of <Helm version>:<filepath>, e.g. v3:/my/path.yaml. Adding all entries to the same file and/or secret is thus not a requirement.

Hint

For the Helm chart, this all can be done by setting configureRepositories.enable to true, it will automatically pick up the flux-helm-reposities secret created earlier in this guide and configure the --helm-repository-import flag for the enabled Helm versions. The certificate secret can be mounted by configuring the extraVolumes and extraVolumeMounts values.

Extending the supported Helm repository protocols

By default, the Helm Operator is able to pull charts from repositories using HTTP/S. It is however possible to extend the supported protocols by making use of a Helm downloader plugin, this allows you for example to use charts hosted on Amazon S3 or Google Cloud Storage.

Installing a Helm downloader plugin

The easiest way to install a plugin so that it becomes accessible to the Helm operator to use an init container and one of the available helm binaries in the Helm Operator's image and a volume mount. For the Helm chart, refer to the chart the documentation.

Plugin folder paths per Helm version:

Version Plugins Config
Helm 2 /var/fluxd/helm/cache/plugins /var/fluxd/helm/plugins
Helm 3 /root/.cache/helm/plugins /root/.local/share/helm/plugins

Add a volume entry of type emptyDir to the deployment of your Helm Operator, this is where the plugins will be stored for the lifetime duration of the pod:

spec:
 volumes:
 - name: helm-plugins-cache
   emptyDir: {}

Next, add a new init container that uses the same image as the Helm operator's container, and makes use of the earlier mentioned volume, with correct volume mounts for the Helm version you are making use of. The available helm2 and helm3 binaries can then be used to install the plugin:

spec:
 initContainers:
 - name: helm-3-downloader-plugin
   image: docker.io/fluxcd/helm-operator:<tag>
   imagePullPolicy: IfNotPresent
   command:
     - 'sh'
     - '-c'
     # Replace '<plugin>' and '<version>' with the respective
     # values of the plugin you want to install
     - 'helm3 plugin install <plugin> --version <version>'
   volumeMounts:
   - name: helm-plugins-cache
     # See: 'plugin folder paths per Helm version'
     mountPath: /root/.cache/helm/plugins
     subPath: v3
   - name: helm-plugins-cache
     # See: 'plugin folder paths per Helm version'
     mountPath: /root/.local/share/helm/plugins
     subPath: v3-config

Last, add the same volume mounts to the Helm Operator container so that the downloaded plugin becomes available:

spec:
 containers:
 - name: flux-helm-operator
   image: docker.io/fluxcd/helm-operator:<tag>
   ...
   volumeMounts:
   - name: helm-plugins-cache
     # See: 'plugin folder paths per Helm version'
     mountPath: /root/.cache/helm/plugins
     subPath: v3
   - name: helm-plugins-cache
     # See: 'plugin folder paths per Helm version'
     mountPath: /root/.local/share/helm/plugins
     subPath: v3-config

Using an installed protocol in your HelmRelease

Once a Helm downloader plugin has been successfully installed, the newly added protocol can be used in the .chart.repository value of a HelmRelease:

spec:
  chart:
    repository: s3://bucket-name/charts
    name: chart-name
    version: 1.0.0

Caution

Most downloader plugins expect some form of credentials to be present to be able to download a chart, make sure those are available in the Helm operator's container before attempting to make use of the newly added protocol.

Git repositories

Besides the extensive support for Helm repositories, the Helm Operator also offers support for charts from Git repository sources. You can refer to a chart from a Git repository, rather than a Helm repository, with a .chart section like this:

spec:
  chart:
    git: [email protected]:org/repo
    ref: master
    path: charts/podinfo

The definition of the listed keys is as follows:

  • git: The URL of the Git repository, e.g. [email protected]:org/repo or https://github.com/org/repo.git.

Note: specifying a custom port only works when the protocol is specified, e.g. ssh://[email protected]:2222/org/repo.git and not [email protected]:2222/org/repo. * ref (Optional): The Git reference, e.g. a branch, tag, or (short) commit hash. When omitted, defaults to master or the configured --git-default-ref. * path: The path of the chart relative to the root of the Git repository.

In this case, the Helm Operator will start a mirror for the Git repository, and a temporary working clone at the current HEAD of the defined ref of the mirror will be created, before performing a release with the path given.

Mirrored Git repositories are polled for changes by fetching from the upstream on the configured --git-poll-interval (defaults to 5 minutes). When a change is detected the Helm Operator will collect all HelmRelease resources making use of the mirror, and inspect if the change updates the chart at the path given. When this is true, it will schedule a new release and an upgrade will follow.

When a temporary working clone cannot be created due to e.g. the mirror not being available yet or a cloning failure because of missing credentials, a status condition of type ChartFetched will be recorded on the HelmRelease resource with the returned error.

Note

You can pin a chart to a specific version by changing the .ref to a tag or commit hash.

Authentication

Unauthenticated cloning from Git repositories is possible for public Git repositories by making the Helm Operator fetch them over HTTP/S. It is however likely that most of the time you will be using a Git repository chart source, some form of authentication is required before the repository can be accessed by the Helm Operator.

Tip

Because the Helm Operator does not perform any write operations on the Git repository, credentials with read permissions are always sufficient.

SSH

For Git over SSH the Helm Operator makes use of private keys available in the container. Because of this, any HelmRelease under the management of a Helm Operator instance has access to the same repositories once a private key has been provided and no additional configuration is required for the resource itself other than defining the Git repository in the .chart.repo.

To provide a private key to be used for Git operations over SSH, put the key in a secret under the entry identity:

kubectl create secret generic flux-git-deploy \
    --from-file=identity=<path to key file>

Next, mount it into the Helm Operator container as shown in the example deployment.

The default ssh_config that ships with the Helm Operator's Docker image expects an identity file at /etc/fluxd/ssh/identity, which is where it will be if you just uncomment the blocks from the example.

Providing multiple private keys

If you are using more than one repository, you may need to provide more than one private key. In that case, you can create a secret with an entry for each key and mount that as well as an ssh_config file mentioning each key as an IdentityFile in /root/.ssh.

For example, to provide different credentials for github.com and bitbucket.org you would create a ssh_config file looking like this:

Host github.com
    HostName github.com
    User git
    IdentityFile <github private key path>
    IdentitiesOnly yes

Host bitbucket.org
    HostName bitbucket.org
    User git
    IdentityFile <bitbucket private key path>
    IdentitiesOnly yes

Note

The IdentitiesOnly ensures that only the IdentityFile for the Host is used and any other identity files known are ignored.

Multiple private keys for Git repositories on the same host

There is one caveat to the example illustrated above; due to the fact that permissions are being handled by the Git server and not SSH itself, any public key known to the Git server will result in a successful login while the private counterpart it belongs to may not actually have access to the Git repository that is targeted. This poses a problem when you have multiple repositories on the same Git server with a dedicated private key per repository.

The workaround is to use an alias for the Host value, and then use this as a replacement for the hostname in the defined Git repository URL of the HelmRelease:

Host github-repository1
    HostName github.com
    User git
    IdentityFile <repository specific private key path>
    IdentitiesOnly yes
spec:
  chart:
    git: [email protected]:org/repo
    ref: master
    path: charts/podinfo

HTTPS

For Git over HTTPS the Helm Operator offers two ways of providing credentials.

Per-resource credentials using .chart.secretRef

To provide HTTPS credentials per HelmRelease resource you can make use of a secretRef in the .chart and a secret with a username and password. The defined secret is retrieved from Kubernetes and appended to the .chart.git URL before starting the Git mirror.

First, create a secret with the username and password that give access to the Git repository:

kubectl create secret generic git-https-credentials \
    --from-literal=username=<username> \
    --from-literal=password=<password>

Now, add the reference to the secret to the .chart:

spec:
  chart:
    git: https://github.com/org/repo
    ref: master
    path: charts/podinfo
    secretRef:
      name: git-https-credentials
Global credentials using .netrc

It is also possible to provide HelmRelease resources access to global credentials via a .netrc file mounted in the /root/ directory of the Helm Operator container.

Caution

This approach suffers essentially from the same caveat as mentioned for Git over SSH.

To provide credentials for github.com, you would create a .netrc file like this:

machine github.com
login <username>
password <password>

After mounting the file from a secret, you can then define the plain HTTPS URL of the Git repository in your HelmRelease:

spec:
  chart:
    git: https://github.com/org/repo.git
    ref: master
    path: charts/podinfo

Dependency updates

For a chart from a Git repository the Helm Operator runs a dependency update by default, this is done through an action that equals to helm dep update. You may want to disable this behaviour, for example because your dependencies are already in git, to do so set skipDepUpdate to true in .chart:

spec:
  chart:
    git: [email protected]:org/repo
    ref: master
    path: charts/podinfo
    skipDepUpdate: true

Notifying the Helm Operator about Git changes

As earlier laid out in this guide the Helm Operator fetches the upstream of mirrored Git repositories on the configured --git-poll-interval (defaults to 5 minutes). In some scenarios (think CI/CD), you may not want to wait for this interval to pass.

To help you with this the Helm Operator serves a HTTP API endpoint to instruct it to immediately refresh all Git mirrors:

$ kubectl port-forward deployment/flux-helm-operator 3030:3030 &
$ curl -XPOST http://localhost:3030/api/v1/sync-git
OK

Warning

The HTTP API has no built-in authentication, this means you either need to port forward before making the request or put something in front of it to serve as a gatekeeper.