Chart Hooks

Helm chart will do some extra actions beside creating k8s objects. For example, helm chart can send email before upgrading and after upgrading. These extra actions called as hooks.

Helm Life cycle is "helm install -> verify -> render -> install"

Hooks are in two categories. 1. Pre 2. Post

Annotations	Description
pre-install	Executes after templates are rendered and before any k8s resources are created
pre-upgrade	Executes on an upgrade request after templates are rendered, but before any resources are updated
pre-delete	Executes on a deletion request before any resources are deleted from Kubernetes
pre-rollback	Executes on a rollback request after templates are rendered, but before any resources are rolled back
post-install	Executes after all resources are loaded into Kubernetes
post-upgrade	Executes on an upgrade request after all resources have been upgraded
post-delete	Executes on a deletion request after all of the release's resources have been deleted
post-rollback	Executes on a rollback request after all resources have been modified

job.yaml

apiVersion: batch/v1
kind: Job
metadata:
  name: hello
  annotations:
    # This is what defines this resource as a hook. Without this line, the
    # job is considered part of the release.
    "helm.sh/hook": pre-install
spec:
  template:
    spec:
      containers:
      - name: hello
        image: busybox:1.28
        command: 
        - /bin/sh
        - -c
        - date; echo Pre-install hook is successful
      restartPolicy: OnFailure

The above resource will be executed before all k8s objects are created because the above resource file has pre-install hook.

Remember that we can have multiple hook in the manifest file.

annotations:
  "helm.sh/hook": post-install,post-upgrade

If we are having multiple hooks, then their order of execution is defined based on weight. Weight must be a string and it can be negative or positive values. Order of execution is always in ascending order.

annotations:
  "helm.sh/hook-weight": "5"

Hook Deletion Policy

annotations:
  "helm.sh/hook-delete-policy": before-hook-creation,hook-succeeded

Annotations	Description
before-hook-creation	Delete the previous resource before a new hook is launched (default)
hook-succeeded	Delete the resource after the hook is successfully executed
hook-failed	Delete the resource if the hook failed during execution

job.yaml

apiVersion: batch/v1
kind: Job
metadata:
  name: hello
  annotations:
    # This is what defines this resource as a hook. Without this line, the
    # job is considered part of the release.
    "helm.sh/hook": pre-install
    "helm.sh/hook-deletion-policy": hook-succeeded
spec:
  template:
    spec:
      containers:
      - name: hello
        image: busybox:1.28
        command: 
        - /bin/sh
        - -c
        - date; echo Pre-install hook is successful
      restartPolicy: OnFailure

hook is configured as pre-install and hook deletion policy is as hook-succeeded.

In the above snapshot, job pod is created before all k8s resources are created, and once it is successful, it is automatically deleted as the hook deletion policy is defined as hook-succeeded.