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Templates

The template fields of the ApplicationSet spec are used to generate Argo CD Application resources.

Template fields

An Argo CD Application is created by combining the parameters from the generator with fields of the template (via {{values}}), and from that a concrete Application resource is produced and applied to the cluster.

Here is the template subfield from a Cluster generator:

# (...)
 template:
   metadata:
     name: '{{cluster}}-guestbook'
   spec:
     source:
       repoURL: https://github.com/infra-team/cluster-deployments.git
       targetRevision: HEAD
       path: guestbook/{{cluster}}
     destination:
       server: '{{url}}'
       namespace: guestbook

The template subfields correspond directly to the spec of an Argo CD Application resource:

  • project refers to the Argo CD Project in use (default may be used here to utilize the default Argo CD Project)
  • source defines from which Git repostory to extract the desired Application manifests
    • repoURL: URL of the repository (eg https://github.com/argoproj/argocd-example-apps.git)
    • targetRevision: Revision (tag/branch/commit) of the repository (eg HEAD)
    • path: Path within the repository where Kubernetes manifests (and/or Helm, Kustomize, Jsonnet resources) are located
  • destination: Defines which Kubernetes cluster/namespace to deploy to
    • name: Name of the cluster (within Argo CD) to deploy to
    • server: API Server URL for the cluster (Example: https://kubernetes.default.svc)
    • namespace: Target namespace in which to deploy the manifests from source (Example: my-app-namespace)

Note:

  • Referenced clusters must already be defined in Argo CD, for the ApplicationSet controller to use them
  • Only one of name or server may be specified: if both are specified, an error is returned.

The metadata field of template may also be used to set an Application name, or to add labels or annotations to the Application.

While the ApplicationSet spec provides a basic form of templating, it is not intended to replace the full-fledged configuration management capabilities of tools such as Kustomize, Helm, or Jsonnet.

Generator templates

In addition to specifying a template within the .spec.template of the ApplicationSet resource, templates may also be specified within generators. This is useful for overriding the values of the spec-level template.

The generator's template field takes precedence over the spec's template fields:

  • If both templates contain the same field, the generator's field value will be used.
  • If only one of those templates' fields has a value, that value will be used.

Generator templates can thus be thought of as patches against the outer spec-level template fields.

apiVersion: argoproj.io/v1alpha1
kind: ApplicationSet
metadata:
  name: guestbook
spec:
  generators:
  - list:
      elements:
        - cluster: engineering-dev
          url: https://kubernetes.default.svc
      template:
        metadata: {}
        spec:
          project: "default"
          source:
            revision: HEAD
            repoURL: https://github.com/argoproj-labs/applicationset.git
            # New path value is generated here:
            path: 'examples/template-override/{{cluster}}-override'
          destination: {}

  template:
    metadata:
      name: '{{cluster}}-guestbook'
    spec:
      project: "default"
      source:
        repoURL: https://github.com/argoproj-labs/applicationset.git
        targetRevision: HEAD
        # This 'default' value is not used: it is is replaced by the generator's template path, above
        path: examples/template-override/default
      destination:
        server: '{{url}}'
        namespace: guestbook
(The full example can be found here.)

In this example, the ApplicationSet controller will generate an Application resource using the path generated by the List generator, rather than the path value defined in .spec.template.