GitOps the Hard Way, with Argo CD

Using Multiple Sources for a Single Application

Overriding a value or two with parameters is fine. The problem is what happens as the list grows: every override lives inline in the Application manifest, so the thing that should be reviewable configuration ends up buried in a Kubernetes resource that nobody wants to read.

apiVersion: argoproj.io/v1alpha1
kind: Application
metadata:
  name: todo-app
  namespace: argocd
spec:
  destination:
    namespace: default
    server: https://kubernetes.default.svc
  project: default
  source:
    chart: todo
    repoURL: $HELM_REPO_URL
    targetRevision: 0.2.0
    helm:
      parameters:
      - name: replicaCount
        value: '5'
      - name: service.port
        value: '5000'
      - name: resources.limits.memory
        value: '256Mi'
      # ...and so on for every value you need to change
      valueFiles:
      - values.yaml
  syncPolicy:
    automated:
      prune: true
      selfHeal: true
      allowEmpty: true

This is where Applications turn unmanageable. The better approach is to pull the overrides out of the Application and into a values file in Git, then point the Application at two sources: the chart from the Helm registry, and the values file from your Git repo. The overrides become a normal file you can diff, review in a merge request, and roll back, instead of inline YAML.

The mechanism is Argo CD's multi-source support (spec.sources, plural). One source is tagged with a ref name and contributes no manifests of its own; it just exposes its files. The Helm source then reads a values file out of it using $/path.

Here is how we proceed:

• Create a values-override.yaml in the Git repository.
• Put the values we want to override in that file.
• List two sources on the Application: the Git repo (as a ref) and the Helm chart.

Copy the chart's values as a starting point:

cp $HOME/todo/app/manifests/helm/todo/values.yaml \
  $HOME/todo/app/manifests/values-override.yaml

Set replicaCount to 2 so we can see the override take effect:

cat < $HOME/todo/app/manifests/values-override.yaml
replicaCount: 2
EOF