3. Resource Hooks

In this Lab you are going to learn about Resource Hooks .

Resource Hooks

Hooks allow to run scripts before, during and after the Argo CD sync operation is running. They give you more control over the sync process. They can also run when the sync operation fails for example. The concept is very similar to the concept of Helm Hooks . Argo CD supports many Helm hooks by mapping the Helm annotations onto Argo CD’s own hook annotations. You can see the full mapping of the Helm hooks in the ArgoCD documentation

Some examples when hooks can be useful:

• PreSync hook. Upgrading a Database, Performing a migration before deploying a new version of the application.
• PostSync hook. Run integration, smoke and other tests after the deployment to verify its status.
• Sync hook. Allows to run more complex deployment strategies. e.g.: Blue-Green or Canary Deployments
• SyncFail hook. Clean up a failed deployment.

Hooks are annotated argocd.argoproj.io/hook: <hook> Kubernetes resources in the source repository, which Argo CD will apply during the sync operation.

A PreSync Hook to run a database migration might therefore look like this:

apiVersion: batch/v1
kind: Job
metadata:
  generateName: schema-migrate-
  annotations:
    argocd.argoproj.io/hook: PreSync
...

It’s basically a Kubernetes Job which starts a Pod that executes some sort of code.

Hook Deletion Policies

The hook deletion policy defines when a hook should be deleted. It’s also configured with an annotation argocd.argoproj.io/hook-delete-policy on the hook resource.

apiVersion: batch/v1
kind: Job
metadata:
  generateName: schema-migrate-
  annotations:
    argocd.argoproj.io/hook: PreSync
    argocd.argoproj.io/hook-delete-policy: HookSucceeded
...

• HookSucceeded: will be deleted after the hook succeeded
• HookFailed: will be deleted after a hook failed
• BeforeHookCreation: Any hook resource will be deleted before the new one is created.

Task 3.1: Hook Example

In this task we’re going to deploy an example which has pre and post hooks.

Create the new application argo-hook-$USER with the following command. It will create a service, a deployment and two hooks as soon as the application is synced.

• PreSync: before Job
• Sync: Deployment with name pre-post-sync-hook
• PostSync: after Job

argocd app create argo-hook-$USER --repo https://gitea.training.cluster.acend.ch/$USER/argocd-training-examples.git --path 'pre-post-sync-hook' --dest-server https://kubernetes.default.svc --dest-namespace $USER

Sync the application

argocd app sync argo-hook-$USER

And verify the deployment:

kubectl get pod --namespace $USER --watch

Or in the web UI.

Task 3.2: Post-hook Curl (Optional)

Alter the post sync hook command from sleep to curl https://acend.ch (Could be used to send a notification to a Chat channel) The curl command is not available in the minimal quay.io/acend/example-web-go image. You can use quay.io/acend/example-web-python or different image.

Edit the hook under pre-post-sync-hook/post-sync-job.yaml accordingly, commit and push the changes and trigger the sync operation.

apiVersion: batch/v1
kind: Job
metadata:
  name: after
  annotations:
    argocd.argoproj.io/hook: PostSync
    argocd.argoproj.io/hook-delete-policy: HookSucceeded
spec:
  template:
    spec:
      containers:
      - name: sleep
        image: quay.io/acend/example-web-python
        command: ["curl", "https://acend.ch"]
      restartPolicy: Never
  backoffLimit: 0

Task 3.3: Delete the Application

Delete the application after you’ve explored the Argo CD Resources and the managed Kubernetes resources.

argocd app delete argo-hook-$USER