writing-helmfile.md

The Helmfile Best Practices Guide

This guide covers the Helmfile’s considered patterns for writing advanced helmfiles. It focuses on how helmfile should be structured and executed.

Missing keys and Default values

helmfile tries its best to inform users for noticing potential mistakes.

One example of how helmfile achieves it is that, helmfile fails when you tried to access missing keys in environment values.

That is, the following example let helmfile fail when you have no eventApi.replicas defined in environment values.

{{ .Environment.Values.eventApi.replicas | default 1 }}

In case it isn't a mistake and you do want to allow missing keys, use the getOrNil template function:

{{ .Environment.Values | getOrNil "eventApi.replicas" }}

This result in printing <no value in your template, that may or may not result in a failure.

If you want a kind of default values that is used when a missing key was referenced, use default like:

{{ .Environment.Values | getOrNil "eventApi.replicas" | default 1 }}

Now, you get 1 when there is no eventApi.replicas defined in environment values.

Release Template / Conventional Directory Structure

Introducing helmfile into a large-scale project that involes dozens of releases often results in a lot of repetitions in helmfile.yaml files.

The example below shows repetitions in namespace, chart, values, and secrets:

releases:
# *snip*
- name: heapster
  namespace: kube-system
  chart: stable/heapster
  version: 0.3.2
  values:
  - "./config/heapster/values.yaml"
  - "./config/heapster/{{ .Environment.Name }}.yaml"
  secrets:
  - "./config/heapster/secrets.yaml"
  - "./config/heapster/{{ .Environment.Name }}-secrets.yaml"

- name: kubernetes-dashboard
  namespace: kube-system
  chart: stable/kubernetes-dashboard
  version: 0.10.0
  values:
  - "./config/kubernetes-dashboard/values.yaml"
  - "./config/kubernetes-dashboard/{{ .Environment.Name }}.yaml"
  values:
  - "./config/kubernetes-dashboard/secrets.yaml"
  - "./config/kubernetes-dashboard/{{ .Environment.Name }}-secrets.yaml"

This is where Helmfile's advanced feature called Release Template comes handy.

It allows you to abstract away the repetitions in releases into a template, which is then included and executed by using YAML anchor/alias:

templates:
  default: &default
    chart: stable/{{`{{ .Release.Name }}`}}
    namespace: kube-system
    # This prevents helmfile exiting when it encounters a missing file
    # Valid values are "Error", "Warn", "Info", "Debug". The default is "Error"
    # Use "Debug" to make missing files errors invisible at the default log level(--log-level=INFO)
    missingFileHandler: Warn
    values:
    - config/{{`{{ .Release.Name }}`}}/values.yaml
    - config/{{`{{ .Release.Name }}`}}/{{`{{ .Environment.Name }}`}}.yaml
    secrets:
    - config/{{`{{ .Release.Name }}`}}/secrets.yaml
    - config/{{`{{ .Release.Name }}`}}/{{`{{ .Environment.Name }}`}}-secrets.yaml

releases:
- name: heapster
  <<: *default
- name: kubernetes-dashboard
  <<: *default

See the issue 428 for more context on how this is supposed to work.

Layering

You may occasionally end up with many helmfiles that shares common parts like which repositories to use, and whichi release to be bundled by default.

Use Layering to extract the common parts into a dedicated library helmfiles, so that each helmfile becomes DRY.

Let's assume that your helmfile.yaml looks like:

{ readFile "commons.yaml" }}
---
{{ readFile "environments.yaml" }}
---
releases:
- name: myapp
  chart: mychart

Whereas commons.yaml contained a monitoring agent:

releases:
- name: metricbaet
  chart: stable/metricbeat

And environments.yaml contained well-known environments:

environments:
  development:
  production:

At run time, template expressions in your helmfile.yaml are executed:

releases:
- name: metricbaet
  chart: stable/metricbeat
---
environments:
  development:
  production:
---
releases:
- name: myapp
  chart: mychart

Resulting YAML documents are merged in the order of occurrence, so that your helmfile.yaml becomes:

environments:
  development:
  production:

releases:
- name: metricbaet
  chart: stable/metricbeat
- name: myapp
  chart: mychart

Great!

Now, repeat the above steps for each your helmfile.yaml, so that all your helmfiles becomes DRY.