Helm

kr8 can render helm charts locally and inject parameters as helm values. This provides a great degree of flexibility when installing components into clusters.

Taskfile

An example taskfile for a helm chart might look like this:

version: 2

vars:
  CHART_VER:  v0.8.1
  CHART_NAME: cert-manager

tasks:
  fetch:
    desc: "fetch component dependencies"
    cmds:
      - rm -fr charts vendored; mkdir charts vendored
      # add the helm repo and fetch it locally into the charts directly
      - helm fetch --repo https://charts.jetstack.io --untar --untardir ./charts --version "{{.CHART_VER}}" "{{.CHART_NAME}}"
      - wget --quiet -N https://raw.githubusercontent.com/jetstack/cert-manager/release-0.8/deploy/manifests/00-crds.yaml -O - | grep -v ^# > vendored/00cert-manager-crd.yaml


  generate:
    desc: "generate"
    cmds:
      - kr8-helpers clean-output
      - kr8-helpers yaml-install vendored/00cert-manager-crd.yaml
      - kr8-helpers jsonnet-render 00namespace.jsonnet
      - kr8-helpers helm-render "{{.CHART_NAME}}"

Params

The params.jsonnet for a helm chart directory should include the helm values you want to use. Here's an example:

{
  release_name: 'cert-manager',
  namespace: 'cert-manager',
  kubecfg_gc_enable: true,
  kubecfg_update_args: '--validate=false',
  helm_values: {
    webhook: { enabled: false },  // this is a value for the helm chart
  },
}

Values file

A values file is a required file for a helm component. The name of the file must be componentname-values.jsonnet (for example: cert-manager-values.jsonnet). It's content would be something like this:

local config = std.extVar('kr8');

if 'helm_values' in config then config.helm_values else {}

You can also optionally set the values for the helm chart in here, this would look something like this:

{
  replicaCount: 2
}

Patches

There are certain situations where a configuration option is not available for a helm chart, for example, you might want to add an argument that hasn't quite made it into the helm chart yet, or add something like pod affinity where it isn't actually a value option in a helm chart.

kr8 helps you in this situation by providing a mechanism to patch a helm chart. You need to use the helm-render-with-patch helper and provide a patches.jsonnet in the component directory.

Here's an example patches.jsonnet for external-dns

local apptio = import 'apptio.libsonnet';
local helpers = import 'helpers.libsonnet';  // some helper functions
local kube = import 'kube.libsonnet';
local config = std.extVar('kr8'); // config is all the config from params.jsonnet

// remove Secret objects and add a namespace
[
  for object in helpers.list(
    // object list is converted to hash of named objects, then they can be modified by name
    helpers.named(helpers.helmInput) + {
      ['Deployment/' + config.release_name]+: helpers.patchContainer({
        // Injects an extra arg, which wasn't originally in the helm chart
        [if std.objectHas(config,'assumeRoleArn') then 'args']+: ['--aws-assume-role='+config.assumeRoleArn],
      }),
    },
  )
]