Detailed Resource Show

https://blueprints.launchpad.net/heat/+spec/detailed-resource-show

After creating a stack, there is currently no way to retrieve a resource’s attributes other than outside of heat (e.g. a user can get the ID of a nova server and call nova directly to get such attributes).

Problem description

Currently a template author needs to explicitly define in the outputs section which attributes they’ll need access to after a stack is created. Without doing so, the attributes cannot be retrieved anymore unless the user updates the template to add such attributes to the outputs section and update the stack afterwards.

Proposed change

Since the attributes of a resource are really being retrieved by heat using the resource client, that means the user can get the resource ID from heat and interact directly with the client (e.g. get the ID of a nova server and talk directly to nova) to retrieve its attributes.

We propose returning all resource attributes when displaying data for a specific resource. This way, a user will be able to issue a resource-show call and be able to look up attributes after creating their stacks even if the template author didn’t think about them beforehand.

Because these attributes can be retrieved either by the resource’s client or by changing the template and adding them to the outputs section, this should not pose any more risk of revealing sensitive data than what is already possible.

This can be achieved by changing the API response to also include attributes that can be automatically discovered (i.e. resources that have an attributes schema).

# API # the call below would also return all attributes in the resource schema /<tenant_id>/stacks/<stack_name>/<stack_id>/resources/<resource_name>

However, some resources have dynamic attributes that cannot be discovered using their attributes schema, so this approach won’t work for those resources. For instance, OS::Heat::ResourceGroup has dynamic attributes based on what outputs/attributes the group type exposes and OS::Heat::SoftwareDeployments has an attribute for each output defined in the config resource outputs property.

For such resources, the API can be extended to accept a query param that will hold the names of the attributes to be retrived. Something like:

# API

/<tenant_id>/stacks/<stack_name>/<stack_id>/resources/ <resource_name>?with_attr=foo&with_attr=bar

# heatclient

resource-show <stack_name> <resource_name> –with-attr foo –with-attr bar

However, certain clients or scripts may want to consume a given attribute directly. For these cases, we could also add two new endpoints: one to keep things RESTful and return only the discoverable attributes of a resource; and another one that would only return the value of the requested attribute.

# API

/<tenant_id>/stacks/<stack_name>/<stack_id>/resources/<resource_name>/ attributes

/<tenant_id>/stacks/<stack_name>/<stack_id>/resources/<resource_name>/ attributes/<attribute_name>

# heatclient

heat resource-attributes <stack-id> <resource-name>

heat resource-attributes <stack-id> <resource-name> <attribute-name>

Alternatives

Alternatively, we can keep the current resource-show behavior the same and only add the two new endpoints to return the attribute information. This has the benefit of being simpler to implement, as only changes to add the new endpoint would be needed. However, the drawback is that one would have to make two separate calls to get all the available information on a given resource: one to resource-show and another one to resource-attributes.

Implementation

Assignee(s)

Primary assignee:
andersonvom asifrc

Milestones

Target Milestone for completion:
Kilo

Work Items

  • Add resource attributes to the engine API at format time.

Dependencies

None

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