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Introduction to ArgoCD

Learning Goals

  • Update applications in ArgoCD.
  • Understand the difference between Refresh and Sync in ArgoCD.
  • Use the Diff feature in the ArgoCD UI.
  • Update replicas using kubectl and understand the implications on the source of truth.
  • Rollback to a previous application state.
  • Troubleshoot and resolve issues with faulty manifests.

Introduction

In this exercise, you will be diving deeper into the management of applications using ArgoCD.

Exercise

Overview

In this exercise, you will:

  • Update the quotes-flask application.
  • Explore the difference between Refresh and Sync in ArgoCD.
  • Use the Diff feature in the ArgoCD UI.
  • Update replicas of the application using kubectl.
  • Rollback to a previous state of the application.
  • Troubleshoot a faulty manifest and resolve the issue.

💡 Understanding Refresh vs. Sync

  • Refresh: This action updates the live view in ArgoCD with the current state of the cluster and the state of the git repo. It does not change any resources in the cluster.
  • Sync: This action deploys the desired state from the Git repository to the cluster. If there are differences between the Git repo and the cluster, Sync will make the necessary changes to align them.

Step by Step Instructions

More Details

Tasks

Updating the Application

  • In the terminal, type kubectl get all to see that even though we have made the application manifest, the application is not yet deployed to the cluster.
  • In the ArgoCD UI, select your quotes-flask application.
  • Click on Refresh and observe that the live view is updated, but the application state remains unchanged.
  • Click on Sync and confirm with Synchronize to deploy the changes you made in the repository to the cluster.
  • Notice how all the resources in the UI are now turning from yellow to green, indicating that the application is in a healthy state.
  • In the terminal, type kubectl get all to see that the application is now deployed to the cluster.
NAME                            READY   STATUS    RESTARTS   AGE
pod/backend-5cd66f88c-bp6xz     1/1     Running   0          8m2s
pod/frontend-6776498dd8-hrjwj   1/1     Running   0          8m2s
pod/postgres-7bc8b45445-btdkx   1/1     Running   0          8m2s

NAME               TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)          AGE
service/backend    ClusterIP   10.100.168.124   <none>        5000/TCP         8m2s
service/frontend   NodePort    10.100.105.77    <none>        5000:30248/TCP   8m2s
service/postgres   ClusterIP   10.100.249.10    <none>        5432/TCP         8m2s

NAME                       READY   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/backend    1/1     1            1           8m2s
deployment.apps/frontend   1/1     1            1           8m2s
deployment.apps/postgres   1/1     1            1           8m2s

NAME                                  DESIRED   CURRENT   READY   AGE
replicaset.apps/backend-5cd66f88c     1         1         1       8m2s
replicaset.apps/frontend-6776498dd8   1         1         1       8m2s
replicaset.apps/postgres-7bc8b45445   1         1         1       8m2s

Using the Diff Feature in UI

  • Make a change to the quotes-flask application in your GitHub repository in the file quotes-flask/k8s/frontend-deployment.yaml
    • Change the replica count of the frontend deployment to 2.
    • Commit and push the changes to the repository.
  • Go to the ArgoCD UI.
    • Select the quotes-flask application and click on Refresh. This will update the live view in ArgoCD with the current state of the cluster.
    • Click on App Diff. This will show the differences between the live application and the desired state in the Git repository. If the full diff is too long, you click on the compact diff button to see a summary of the changes.
    • Click on Sync and confirm with Synchronize to deploy the changes you made in the repository to the cluster.

Updating Replicas with kubectl

  • Use kubectl to scale the replicas of the quotes-flask application:
kubectl scale deployment frontend --replicas=3
  • In the ArgoCD UI, notice that the application is now OutOfSync because the live state (3 replicas) differs from the desired state in the Git repository.

💡 This demonstrates the importance of maintaining a single source of truth. Manual changes can cause drift from the desired state.

Rolling Back Changes

  • In the ArgoCD UI, select the quotes-flask application.
  • Click on the History and rollback button.
  • Choose a previous successful sync and click Rollback to revert the application to that state.

This can be handy as a quick way to revert changes that were made in error. However, it is not a replacement for a proper GitOps workflow. In a GitOps workflow, you would revert the changes in the Git repository and then sync the application in ArgoCD.

In the later exercises, we will automate the sync process, making ArgCD revert the changes automatically.

Testing Self-Heal Policy

  • In the ArgoCD UI, select the quotes-flask application.

  • Click on app details, scroll down to sync policy and enable Auto-Sync.

  • Use kubectl to make a change to the quotes-flask application (e.g., scale the replicas to 4):

    kubectl scale deployment frontend --replicas=4

  • Verify that there are four replicas:

    kubectl get pods

  • In the ArgoCD UI, notice that the application is now OutOfSync because the live state (4 replicas) differs from the desired state in the Git repository.

  • In the ArgoCD UI, select the quotes-flask application.

  • Then enable the Self Heal section under Sync Policy and click on Save.

Now, if you make a change to the application using kubectl, ArgoCD will automatically revert the change to the desired state defined in the Git repository.

  • Use kubectl to see that ArgoCD has reverted the change:
kubectl get pods
NAME                        READY   STATUS    RESTARTS   AGE
backend-5cd66f88c-mchxn     1/1     Running   0          20h
frontend-6776498dd8-xwjpq   1/1     Running   0          20h
frontend-6776498dd8-zfw5l   1/1     Running   0          20h
postgres-7bc8b45445-kshd8   1/1     Running   1          20h

Troubleshooting Faulty Manifests

  • Intentionally introduce an error in one of the Kubernetes manifests in your GitHub repository (e.g., a typo in a field name).
  • Try to sync the application in ArgoCD. The sync will fail.
  • In the ArgoCD UI, navigate to the Events tab under app details for the quotes-flask application. Here, you can see detailed error messages that will help you identify the issue.
  • Fix the error in the manifest, commit, and push the changes to the repository.
  • Sync the application again in ArgoCD. The sync should now succeed.

Cleanup

Go ahead and delete the app in the ArgoCD UI. We will add it later as a true GitOps application