What are Argo CD Applications and ApplicationSets?

An Application is the fundamental Argo CD custom resource. It maps a single Git source (repository URL, path, revision) to a single Kubernetes destination (cluster API URL, namespace) and declares how to sync between them. One Application typically represents one microservice or one component of a larger system.

An ApplicationSet is a higher-level CR managed by the ApplicationSet controller. Instead of managing one application, it uses generators to programmatically produce multiple Application CRs from a template. As generators produce or remove parameters, the controller creates, updates, or deletes the corresponding Applications automatically.

Built-in ApplicationSet generators:

• List generator: Explicit list of parameter sets — each item creates one Application.
• Git directory generator: Scans a Git repo for directories matching a glob pattern; each directory becomes one Application.
• Cluster generator: Creates one Application per registered Argo CD cluster, optionally filtered by cluster labels.
• Matrix generator: Cross-product of two other generators — e.g., all apps × all clusters.
• Pull-request generator: Creates a temporary Application for each open PR, enabling ephemeral preview environments.

# ApplicationSet using the git directory generator
apiVersion: argoproj.io/v1alpha1
kind: ApplicationSet
metadata:
  name: all-apps
  namespace: argocd
spec:
  generators:
    - git:
        repoURL: https://github.com/org/gitops-config.git
        revision: main
        directories:
          - path: apps/*
  template:
    metadata:
      name: "{{path.basename}}"
    spec:
      project: default
      source:
        repoURL: https://github.com/org/gitops-config.git
        targetRevision: main
        path: "{{path}}"
      destination:
        server: https://kubernetes.default.svc
        namespace: "{{path.basename}}" 

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