Map computed properties from output shape to CRD's status

[kumargauravsharma]

Is your feature request related to a problem?
While populating CRD's status field for ReplicationGroup output shape, the properties like ReplicasPerNodeGroup are not populated/computed. It can be computed using Status.NodeGroups from output shape.

And as the GoCodeSetOutput logic copies the r.ko (desired state) into returned value ko

        // Merge in the information we read from the API call above to the copy of
	// the original Kubernetes object we passed to the function
	ko := r.ko.DeepCopy()

the reconciler fails to identify change in such properties when applied using kubectl apply -f updated_resource.yaml
and no update call is made.

Describe the solution you'd like
Enhance generator.yaml to specify the mapping of output shape properties to CRD's status properties or allowing custom code invocation during GoCodeSetOutput to help services implement the custom logic for such scenarios.

Describe alternatives you've considered
A description of any alternative solutions or features you've considered.

[kumargauravsharma]

Possible solution:
Enhance generator.yaml to specify custom code invocation during GoCodeSetOutput to help services implement the custom logic. This is generic solution which can be used for any service in ACK.

For ElastiCache ReplicationGroup, the updated generator.yaml will look like:

resources:
  ReplicationGroup:
    custom_set_output_operation:
      GoCodeCustomSetOutput

and an implementation for GoCodeCustomSetOutput operation will be provided inside aws-controllers-k8s/services/elasticache/pkg/resource/replication_group/custom_set_output.go file and it will be invoked from crd.go::GoCodeSetOutput.

Thus the fields that are part of resource spec (due to create API input but do not have direct mapping in describe API output) will be properly retrieved from response object and improve the reconciler update code flow to identify changes/diffs in desired, latest states.

[kumargauravsharma]

Considering that different operations (create, read, update) on a custom resource can have different output shapes, the custom set output needs to process output shape; thus updated generator.yaml would look like:

resources:
  ReplicationGroup:
    output_shapes:
      ReplicationGroup:
        custom_set_output_operation: CustomSetReplicationGroupOutput

This can be read as: For resource ReplicationGroup the output shape ReplicationGroup has custom set output operation CustomSetReplicationGroupOutput.

[kumargauravsharma]

Alternative generator.yaml

operations:
  DescribeReplicationGroups:
    custom_set_output_operation: CustomDescribeReplicationGroupsSetOutput
  CreateReplicationGroup:
    custom_set_output_operation: CustomCreateReplicationGroupSetOutput
  ModifyReplicationGroup:
    custom_set_output_operation: CustomModifyReplicationGroupSetOutput

This can be read as: For operation CreateReplicationGroup custom set output operation is CustomCreateReplicationGroupSetOutput

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[RedbackThomson]

Handled through our implementation of hooks aws-controllers-k8s/code-generator#26