feat: get required fields from a list of resources belonging to same Kind

[AmitKumarDas]

ProblemStatement: As a SRE admin, I want to fetch required fields from all resources belonging to the same Kind. For example, I want to fetch spec.replicas from all Deployments with labels my-app: nginx and running in ent namespace.

[AmitKumarDas]

Draft design

kind: Recipe
spec:
  tasks:
  - name: list-replicas-from-deployment
    list:
      state:
        kind: Deployment
        metadata:
          namespace: ent
          labels:
            my-app: nginx
        spec: 
          replicas: ?

• Above when applied will result in below

kind: Recipe
spec:
  # removed for brevity
status:
  tasks:
    list-replicas-from-deployment:
      objectList:
      - kind: Deployment
        metadata:
          name: abc
          namespace: ent
          labels:
            my-app: nginx
        spec: 
          replicas: 2
      - kind: Deployment
        metadata:
          name: zef
          namespace: ent
          labels:
            my-app: nginx
        spec: 
          replicas: 3

NOTES

• We might need to join the fields from multiple tasks

kind: Recipe
spec:
  tasks:
  - name: list-replicas-from-deployment
    list:
      join:
        type: Parent
      state:
        kind: Deployment
        metadata:
          namespace: ent
          labels:
            my-app: nginx
        spec: 
          replicas: ?
  - name: list-cluster-ip-from-service
    list:
      join:
        type: Child
        when: 
        - NameMatch
        - NamespaceMatch
        - AllLabelsMatch
      state:
        kind: Service
        metadata:
          namespace: ent
          labels:
            my-app: nginx
        spec: 
          clusterIP: ?

• Above would extract the corresponding clusterIP
• Since join is enabled it would match against corresponding Parent task output
• If match is successful clusterIP is made available in the list-replicas-from-deployment output
• If no match then clusterIP is made available in the list-cluster-ip-from-service output
• NOTE: Task with join.type as Parent should appear before all Child tasks
• NOTE: There should be only one task with join.type as Parent
• NOTE: There can be multiple tasks with join.type as Child