Step 1: Understanding Helm Hooks
Helm hooks are a feature introduced in Helm 2.0 that allows you to perform actions during the release lifecycle of a Helm chart. Hooks can be used to execute scripts, run commands, or trigger other actions at specific points in the release process. Helm supports several types of hooks, including pre-install, post-install, pre-upgrade, post-upgrade, pre-delete, and post-delete hooks.
Hooks is a helm feature that allows helm to launch resources into the cluster in response to helm lifecycle events (such as a chart being installed). All it takes to turn a regular Kubernetes object into a helm hook is to apply an annotation that indicates which lifecycle event the object should be tied to.
Helm hooks provide a way to apply certain Kubernetes resources (usually Jobs) at a particular stage of a deployment. Most developers leverage hooks to:
- Load a ConfigMap or Secret during install before any other charts are loaded
- Execute a Job to back up a database before installing a new chart and a second job to restore the data in the database
- Run a job before deleting a release to gracefully take out a service before completely removing it
Hook works like a regular template, but they have special annotations that cause helm to utilize them differently. In this section, we will cover the basic usage pattern for hooks.
We can define Helm hooks that will be executed at these points in the release’s lifecycle:
- pre-install – Before the release is installed.
- post-install – After the release is installed
- pre-delete – Before the release is uninstalled.
- post-delete – After the release is uninstalled.
- pre-upgrade – Before the release is upgraded.
- post-upgrade – After the release is upgraded.
- pre-rollback – Before the release is rolled back to a previous version.
- post-rollback – After the release is rolled back to a previous version.
Helm Hook
Hooks is a helm feature that allows helm to launch resources into the cluster in response to helm lifecycle events (such as a chart being installed). All it takes to turn a regular Kubernetes object into a helm hook is to apply an annotation that indicates which lifecycle event the object should be tied to.
Helm hooks provide a way to apply certain Kubernetes resources (usually Jobs) at a particular stage of a deployment. Most developers leverage hooks to:
- Load a ConfigMap or Secret during install before any other charts are loaded
- Execute a Job to back up a database before installing a new chart and a second job to restore the data in the database
- Run a job before deleting a release to gracefully take out a service before completely removing it
Hook works like a regular template, but they have special annotations that cause helm to utilize them differently. In this section, we will cover the basic usage pattern for hooks.
Step 2: Creating a Helm Chart
Before diving into hooks, let’s assume you have a basic understanding of creating Helm charts. If you’re new to Helm, it’s recommended to familiarize yourself with chart creation first. You can refer to the official Helm documentation for creating a simple chart.
Step 3: Adding a Pre-Install Hook
To add a pre-install hook to your Helm chart, you need to create a templates directory in your chart’s root directory (if it doesn’t exist already). Inside the templates directory, create a YAML file for your hook. For example, let’s create a file named pre-install-hook.yaml.
In the pre-install-hook.yaml file, define the hook using the following structure:
apiVersion: batch/v1
kind: Job
metadata:
name: {{ include "mychart.fullname" . }}-pre-install-hook
labels:
app.kubernetes.io/managed-by: {{ .Release.Service | quote }}
helm.sh/hook: pre-install
helm.sh/hook-weight: "1"
helm.sh/hook-delete-policy: hook-succeeded
spec:
template:
spec:
containers:
- name: {{ .Chart.Name }}
image: busybox
command: ['sh', '-c', 'echo "Running pre-install hook"']
restartPolicy: Never
In this example, we define a Kubernetes Job that runs a container with the busybox image and executes a simple command.
Step 4: Adding a Post-Install Hook
Similar to the pre-install hook, you can add a post-install hook to your chart. Create a new YAML file in the templates directory, for example, post-install-hook.yaml.
In the post-install-hook.yaml file, define the hook using the following structure:
apiVersion: batch/v1
kind: Job
metadata:
name: {{ include "mychart.fullname" . }}-post-install-hook
labels:
app.kubernetes.io/managed-by: {{ .Release.Service | quote }}
helm.sh/hook: post-install
helm.sh/hook-weight: "1"
helm.sh/hook-delete-policy: hook-succeeded
spec:
template:
spec:
containers:
- name: {{ .Chart.Name }}
image: busybox
command: ['sh', '-c', 'echo "Running post-install hook"']
restartPolicy: Never
This hook follows a similar structure as the pre-install hook but with a different name and the helm.sh/hook set to post-install.
Step 5: Updating the Chart’s hooks Section
Now that we have defined our hooks, we need to update the chart’s hooks section in the templates/hooks.yaml file. If the file doesn’t exist, create it.
Add the following code to the hooks.yaml file:
{{- if .Values.hooks.preInstall.enabled -}}
preInstall:
- name: {{ include "mychart.fullname" . }}-pre-install
manifest: {{ include "mychart.pre
Reference
- https://medium.com/@pratyush.mathur/introduction-to-helm-hooks-460c704021b
- https://kodekloud.com/blog/chart-hooks/#
- https://medium.com/@pratyush.mathur/introduction-to-helm-hooks-460c704021b
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