ArgoCD ApplicationSets — K8s SRE Reference

TL;DR

ApplicationSets generate many ArgoCD Applications from a template + generator. Use them for multi-cluster deploys, monorepo app discovery, or Git directory scanning — instead of hand-writing one Application per app.

When to Use

Scenario	Generator
Deploy same app to many clusters	`clusters`
One Application per folder in Git	`git` (directories)
One Application per registered cluster	`clusterDecisionResource` or `clusters`
Matrix of clusters × environments	`matrix` (combine generators)
Explicit list of apps	`list`

Git Directory Generator

Scans a Git repo path and creates one Application per subdirectory — common for monorepos.

yaml applicationset-git.yaml

apiVersion: argoproj.io/v1alpha1
kind: ApplicationSet
metadata:
  name: platform-apps
  namespace: argocd
spec:
  generators:
    - git:
        repoURL: https://github.com/example/platform-apps.git
        revision: main
        directories:
          - path: apps/*
  template:
    metadata:
      name: "{{path.basename}}"
    spec:
      project: platform
      source:
        repoURL: https://github.com/example/platform-apps.git
        targetRevision: main
        path: "{{path}}"
      destination:
        server: https://kubernetes.default.svc
        namespace: "{{path.basename}}"
      syncPolicy:
        automated:
          prune: true
          selfHeal: true
        syncOptions:
          - CreateNamespace=true

Cluster Generator

Deploys the same source to every cluster registered in ArgoCD.

yaml applicationset-clusters.yaml

apiVersion: argoproj.io/v1alpha1
kind: ApplicationSet
metadata:
  name: ingress-all-clusters
  namespace: argocd
spec:
  generators:
    - clusters:
        selector:
          matchLabels:
            env: production
  template:
    metadata:
      name: "ingress-{{name}}"
    spec:
      project: platform
      source:
        repoURL: https://github.com/example/platform-addons.git
        targetRevision: main
        path: ingress-nginx
        helm:
          valueFiles:
            - values-{{metadata.labels.env}}.yaml
      destination:
        server: "{{server}}"
        namespace: ingress-nginx
      syncPolicy:
        syncOptions:
          - CreateNamespace=true

Matrix Generator

The matrix generator combines two generator outputs, such as clusters and environments, to create many Applications from one template. Use it when the same app or add-on must be deployed across multiple clusters with environment-specific values.

yaml applicationset-matrix.yaml

spec:
  generators:
    - matrix:
        generators:
          - clusters:
              selector:
                matchLabels:
                  env: production
          - git:
              repoURL: https://github.com/example/platform-apps.git
              revision: main
              directories:
                - path: apps/*
  template:
    metadata:
      name: "{{path.basename}}-{{name}}"
    spec:
      source:
        repoURL: https://github.com/example/platform-apps.git
        path: "{{path}}"
      destination:
        server: "{{server}}"
        namespace: "{{path.basename}}"

Commands

Use these commands to inspect generated child Applications and confirm whether the ApplicationSet controller is creating, updating, or failing to reconcile them.

bash applicationset.sh

kubectl get applicationsets -n argocd
kubectl describe applicationset platform-apps -n argocd
kubectl get applications -n argocd -l argocd.argoproj.io/application-set-name=platform-apps

# List registered clusters.
argocd cluster list

Gotchas

!Template typos scale badly — a bad template creates broken Applications across all clusters.
!Prune on generated apps — removing a directory from Git deletes the Application and its resources.
!Go templates in metadata.name — must produce valid K8s names; use path.basename not full paths.
!Cluster secrets — clusters generator only works for clusters registered in ArgoCD.