Explode Nested Resources

https://blueprints.launchpad.net/heat/+spec/explode-nested-resources

For many UI use-cases, it is generally resource intensive to list all resources associated with a given stack if that stack includes stack-based resources. It is therefore proposed that resource-list should return all resources associated with a given stack if requested.

Problem description

Currently, resource-list only returns top-level resources of a given stack but does not include resources that are inside of any nested stacks. This makes several use cases difficult or sub-optimal because of the need to make several API calls on resource reference links.

  • When deleting a stack, a UI should be able to present the user with a list of all resources associated with a given stack to avoid confusion about what and why certain resources were deleted due to a stack delete.
  • A user of the API (either via CLI, curl, or other method) wants to be able to quickly and easily list and follow the status of every resource associated with a stack, regardless of a resource’s position in the stack hierarchy.
  • OpenStack dashboard may show an incorrect, confusing topology of resources from a stack because it knows nothing about a nested stack (e.g. a group of servers).

Proposed change

The proposed implementation would add an optional query parameter to the resource-list API method:

nested_depth
Recursion depth to limit the returned resources. This parameter indicates that the user wishes to return nested resources as well as those from the parent stack. Setting this parameter to a number results in the system limiting the recursion depth. A value of 0 has no effect. A value of MAX results in all resources being returned up to max_nested_stack_depth. The system will never recurse farther than max_nested_stack_depth, regardless of the value passed in the parameter.

The Heat service would see this parameter and recurse through all of the nested stacks to the specified depth and flatten the resource list data structure. For resources that exist in nested stacks, the containing nested stack id and parent resource name would also be included.

The resulting response data would look like:

{"resources":
  [
    {
      "resource_name": "db",
      "links": [...],
      "logical_resource_id": "db",
      "resource_status_reason": "state changed",
      "updated_time": "2014-04-15T18:23:35Z",
      "required_by": ["web_nodes"],
      "resource_status": "CREATE_COMPLETE",
      "physical_resource_id": "4974985c-da78-444b-aeb3-9a80baccdd1a",
      "resource_type": "OS::Trove::Instance"
    },
    {
      "resource_name": "lb",
      "links": [...],
      "logical_resource_id": "lb",
      "resource_status_reason": "state changed",
      "updated_time": "2014-04-15T18:30:52Z",
      "required_by": [],
      "resource_status": "CREATE_COMPLETE",
      "physical_resource_id": "229145",
      "resource_type": "Rackspace::Cloud::LoadBalancer"
    },
    {
      "resource_name": "web_nodes",
      "links": [...],
      "logical_resource_id": "web_nodes",
      "resource_status_reason": "state changed",
      "updated_time": "2014-04-15T18:25:10Z",
      "required_by": ["lb"],
      "resource_status": "CREATE_COMPLETE",
      "physical_resource_id": "c3a46e6f-f999-4f9b-a797-3043031d381a",
      "resource_type": "OS::Heat::ResourceGroup"
    },
    {
      "resource_name": "web_node1",
      "links": [...],
      "logical_resource_id": "web_node1",
      "resource_status_reason": "state changed",
      "updated_time": "2014-04-15T18:25:10Z",
      "required_by": ["lb"],
      "resource_status": "CREATE_COMPLETE",
      "physical_resource_id": "c3a46e6f-f999-4f9b-a797-3043031d3811",
      "resource_type": "Rackspace::Cloud::Server",
      "parent": "web_nodes",
      "nested_stack_id": "1234512345"
    },
    {
      "resource_name": "web_node2",
      "links": [...],
      "logical_resource_id": "web_node2",
      "resource_status_reason": "state changed",
      "updated_time": "2014-04-15T18:25:10Z",
      "required_by": ["lb"],
      "resource_status": "CREATE_COMPLETE",
      "physical_resource_id": "c3a46e6f-f999-4f9b-a797-3043031d3822",
      "resource_type": "Rackspace::Cloud::Server",
      "parent": "web_nodes",
      "nested_stack_id": "1234512345"
    }
  ]
}

These changes will primarily reside in:

  • heat.engine.service
  • heat.db
  • heat.api
  • python-heatclient

Alternatives

Currently, each resource that abstracts a nested stack will include a link to the nested stack when viewed with a resource-show. This allows a user to implement this functionality client-side by:

  1. listing all of the resources in the stack
  2. retrieving each resource individually
  3. if the current resource has a link to a nested stack, recurse the resources of that stack and add them to the list/tree

While this offers greater flexibility in how nested resources are listed for the user’s particular use case, its very inefficient for the stated use cases as well as very noisy from a network perspective. This specification does not intend to remove this option, only to provide an alternative to more efficiently satisfy several common use cases while maintaining the existing link traversal method for use cases requiring more control over the display of the resource hierarchy.

Implementation

Assignee(s)

Primary assignee:
randall-burt

Milestones

Target Milestone for completion:
Juno-2

Work Items

  • Update DB API and implementation to accept the nested_depth parameter for resource list and use that in logic to append resources from any nested stacks.
  • Update the engine to accept and then pass the nested_depth parameter to the DB API.
  • Update the API to accept and pass the nested_depth parameter to the engine; try not to have to version the RPC API, please.
  • Update python-heatclient to expose the new flag and properly format the output
  • Add the parameters to the Heat V1 WADL

Dependencies

None

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