ArgoCD: Advanced Usage

Managing Multiple Clusters and Environments#

ArgoCD makes it easy to manage deployments across multiple Kubernetes clusters and environments like dev, staging, and production.

Adding Multiple Kubernetes Clusters#

To add a new cluster to ArgoCD:

argocd cluster add <context-name>

This registers an external Kubernetes cluster, allowing ArgoCD to deploy and manage applications remotely.

Using ApplicationSets for Multi-Cluster Deployments#

ApplicationSets allow you to define applications dynamically across multiple clusters.

apiVersion: argoproj.io/v1alpha1
kind: ApplicationSet
metadata:
  name: multi-cluster-app
spec:
  generators:
    - list:
        elements:
          - cluster: dev
          - cluster: staging
  template:
    metadata:
      name: '{{cluster}}-app'
    spec:
      project: default
      source:
        repoURL: https://github.com/myrepo.git
        path: k8s-manifests
      destination:
        server: '{{cluster}}'
        namespace: default

Apply it with:

kubectl apply -f applicationset.yaml

This will deploy the same application to multiple clusters automatically.

Customizing ArgoCD Behaviors with Sync Hooks#

Sync Hooks allow pre- and post-deployment tasks, such as database migrations, to be executed as part of the deployment process.

Example: PreSync Hook for Database Migrations#

apiVersion: batch/v1
kind: Job
metadata:
  annotations:
    argocd.argoproj.io/hook: PreSync
  name: db-migration
spec:
  template:
    spec:
      containers:
        - name: migrate
          image: myrepo/migrate:latest
      restartPolicy: Never

Apply the hook with:

kubectl apply -f sync-hooks.yaml

This ensures the migration job runs before the main deployment begins.

ArgoCD Plugins and Extension Mechanisms#

ArgoCD supports Config Management Plugins (CMP), allowing customization of how manifests are processed before deployment.

Installing and Configuring a Custom Plugin#

apiVersion: v1
kind: ConfigMap
metadata:
  name: argocd-cmp-plugin
  namespace: argocd
data:
  configManagementPlugins: |
    - name: my-plugin
      generate:
        command: ["/usr/local/bin/my-plugin"]

Apply the plugin configuration:

kubectl apply -f plugin-config.yaml

This custom plugin will be executed whenever ArgoCD processes manifests.

Resource Management (Resource Inclusion/Exclusion)#

ArgoCD allows fine-grained control over which Kubernetes resources are managed and synchronized.

Excluding Certain Resource Types from Sync#

To ignore specific fields (e.g., number of replicas in a Deployment):

spec:
  ignoreDifferences:
    - group: apps
      kind: Deployment
      jsonPointers:
        - /spec/replicas

This ensures that changes to replicas made outside Git do not trigger a sync.

Selecting Only Specific Resources#

To apply ArgoCD sync to a specific set of resources:

spec:
  resourceSelector:
    matchLabels:
      env: production

This ensures only resources labeled as env: production are managed by ArgoCD.

Hands-On Exercise#

1. Deploy an ApplicationSet across multiple clusters
   • Create and apply an ApplicationSet YAML file.
2. Configure PreSync and PostSync hooks
   • Add a hook for a database migration job.
3. Implement and test a custom ArgoCD plugin
   • Configure a custom manifest generator plugin.
4. Exclude specific resources from synchronization
   • Modify the ignoreDifferences field to prevent syncing unwanted changes.

By mastering these advanced features, you’ll unlock the full potential of ArgoCD for large-scale Kubernetes deployments!