4. Sync Phases and Waves

In this Lab you are going to learn about Sync Phases and Waves .

Sync Phases and Waves

At a high-level, Argo CD executes the sync operation in the three phases pre-sync, sync and post-sync.

Within each phase you can have one or more waves, that allows you to ensure certain resources are healthy before subsequent resources are synced.

When Argo CD starts a sync, it orders the resources in the following precedence:

• The phase
• The wave they are in (lower values first)
• By kind (e.g. namespaces first)
• By name

It then determines the number of the next wave to apply. This is the first number where any resource is out-of-sync or unhealthy.

It applies resources in that wave.

It repeats this process until all phases and waves are in-sync and healthy.

How to specify waves and phases

Pre-sync and post-sync can only contain hooks defined on annotations argocd.argoproj.io/hook: PreSync.

You can specify the wave in the sync phase by setting an annotation argocd.argoproj.io/sync-wave. Hooks and resources are assigned to wave zero by default. The wave can be negative, so you can create a wave that runs before all other resources.

Task 4.1: Sync Wave Example

Let’s now get our hands on a sync wave example.

Create the new application argo-wave-$USER with the following command. The Application consist of the following resources, phases and waves:

• PreSync
  • Job: upgrade-sql-schema
• Sync Wave 0
  • Deployment: backend
  • Service: backend
• Sync Wave 1
  • Job: maintenance-page-up
• Sync Wave 2
  • Deployment: frontend
  • Service: frontend
• Sync Wave 3
  • Job: maintenance-page-down

Create a file argocd-wave-application.yaml with the following content and apply it:

apiVersion: argoproj.io/v1alpha1
kind: Application
metadata:
  name: argo-wave-$USER
  namespace: openshift-gitops
spec:
  project: default
  source:
    repoURL: https://gitea.training.cluster.acend.ch/$USER/argocd-training-examples.git
    targetRevision: HEAD
    path: sync-wave
  destination:
    server: https://kubernetes.default.svc
    namespace: $USER

oc apply -f argocd-wave-application.yaml

Sync the application:

And verify the deployment:

oc get pod --namespace $USER --watch

Task 4.2: Delete the Application

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

oc delete application argo-wave-$USER -n openshift-gitops