Automating Helm Charts with Ansible

The Automation Broker works in conjunction with the Kubernetes Service Catalog to make services and applications easily deployable. An end user selects a service to be provisioned, selects a “plan” that describes the level of service (small, large, paid, free, persistent, ephemeral, etc), and then provides any required parameters. In this scenario, Helm charts can be utilized in two possible ways.

  • The Automation Broker’s “helm registry adapter” can inspect a chart repository and make each discovered chart available as a service class. The chart’s values.yaml file is made available as a single parameter for a single default plan.
  • The tool helm2bundle creates a Service Bundle image that includes a specific chart. The image can be modified like any service bundle, including changes to metadata such as those in apb.yml.

This post explores how to use Ansible Automation with the latter option to extend the behavior of a helm bundle.

Terms

service bundle – a container image that represents a service class’s metadata and behavior.

helm bundle – a service bundle that contains a helm chart.

APB – aka Ansible Playbook bundle, a service bundle that uses Ansible Automation.

Automate Chart Input

Helm charts, which take input as a free-form yaml file, can take advantage of Ansible Automation by being included in a helm bundle that is based on the helm-ansible-base image.

For example, the stable/redis chart has a setting in its values.yml that always needs to be changed in order to run in OpenShift. These are the steps to set that automatically based on Ansible facts.

Make the helm bundle

$ helm fetch stable/redis
$ helm2bundle redis-1.1.12.tar.gz

Create overrides template

The helm-ansible-base image knows to look for a file called overrides.yml.j2. If found, it gets rendered using ansible facts and then passed into helm as a settings file. It should be a subset of the values that are settable for the chart, as described in the chart’s values.yaml file.

Ours should look like this:

---

{% set secenabled = false if (cluster == "openshift") else true %}

## Pod Security Context
securityContext:
  enabled: {{ secenabled }}

Change the Dockerfile

Set the base image in the Dockerfile to helm-ansible-base, and add the overrides template file.

FROM ansibleplaybookbundle/helm-ansible-base
LABEL "com.redhat.apb.spec"=""
COPY redis-1.1.12.tgz /opt/chart.tgz
COPY overrides.yml.j2 /opt/overrides.yml.j2
ENTRYPOINT ["entrypoint.sh"]

Summary

If you build and use that Helm Bundle to provision Redis, it will create a new fact based on the value of an existing fact, and then use the new fact to render a helm settings file. Ansible made it easy for us to dynamically configure this setting. While this example is relatively trivial, the same technique can be employed to do much more sophisticated configuration.

In the next blog post, we will use a similar technique to add rich parameters to a helm bundle, so that the user input experience is easier than editing yaml.

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