ApplicationSets and generators

An ApplicationSet uses a generator (list, cluster, Git, matrix) to produce parameters and stamps out one Application per set from a template.

An ApplicationSet is a template plus a generator. The generator produces a list of parameter sets; the ApplicationSet controller renders one Application per set and keeps them in step — adding, updating and (by default) deleting them.

apiVersion: argoproj.io/v1alpha1
kind: ApplicationSet
metadata:
  name: shop-api
  namespace: argocd
spec:
  goTemplate: true
  goTemplateOptions: ["missingkey=error"]
  generators:
    - list:
        elements:
          - { env: dev,     cluster: https://kubernetes.default.svc }
          - { env: staging, cluster: https://kubernetes.default.svc }
          - { env: prod,    cluster: https://prod-sg.example.com:6443 }
  template:
    metadata:
      name: 'shop-api-{{.env}}'
    spec:
      project: shop
      source:
        repoURL: https://github.com/example-org/shop-config.git
        targetRevision: main
        path: 'apps/shop-api/overlays/{{.env}}'
      destination:
        server: '{{.cluster}}'
        namespace: 'shop-{{.env}}'

Generators

Generator	Produces one set per…	Typical use
List	element you write in the YAML	A few fixed environments
Cluster	cluster registered in Argo CD (filter by labels)	Install the same add-on on every cluster
Git directories	folder matching a path, e.g. `apps/*`	One app per folder in a monorepo
Git files	JSON/YAML file, e.g. `envs/*/config.json`	Per-environment parameters kept in Git
Matrix	combination of two generators	Every app × every cluster
Merge	merged result of generators	Defaults plus overrides
Pull request / SCM provider	open PR or repository	Preview environments per PR

generators:
  - matrix:
      generators:
        - git:
            repoURL: https://github.com/example-org/platform-config.git
            revision: main
            directories: [{ path: addons/* }]
        - clusters:
            selector: { matchLabels: { env: prod } }
# template name: '{{.path.basename}}-{{.name}}'

Safety switches

goTemplate: true with missingkey=error fails loudly on a typo instead of creating an app called shop-api-.
syncPolicy.preserveResourcesOnDeletion: true keeps workloads if the ApplicationSet is deleted.
syncPolicy.applicationsSync: create-only (or create-update) stops the controller from deleting Applications when an element disappears.
Generated Applications are owned by the ApplicationSet: edit the template, not the children — manual edits are overwritten.
An ApplicationSet can create Applications in any project its template names, so only platform admins should write ApplicationSets (or restrict them with the applicationset RBAC and allowed projects).

argocd appset create shop-api-appset.yaml
argocd appset list
argocd appset get shop-api