依赖和Cloudformation定制资源

Question

From my understanding a resource that has DependsOn specified should be updated if the resource it depends on is updated. I see this for some resources, but it doesn't seem to be working for a custom resource.

I'm working with APIGateway and trying to use a custom resource to deploy the a stage when the resources related to the stage are updated. This is because the included AWS::ApiGateway::Stage & AWS::ApiGateway::Deployment don't seem to work very well when needed to deploy an update.

I have the following template (snipped for easy reference):

<snip>
pipelineMgrStateMachine:
  Type: AWS::StepFunctions::StateMachine
  Properties:
    <snip>

webhookEndPointMethod:
  Type: AWS::ApiGateway::Method
  DependsOn: pipelineMgrStateMachine
  Properties:
    RestApiId: !Ref pipelineMgrGW
    ResourceId: !Ref webhookEndPointResource
    HttpMethod: POST
    AuthorizationType: NONE
    Integration:
      Type: AWS
      IntegrationHttpMethod: POST
      Uri: !Sub arn:aws:apigateway:${AWS::Region}:states:action/StartExecution
      Credentials: !GetAtt pipelineMgrGWRole.Arn
      PassthroughBehavior: WHEN_NO_TEMPLATES
      RequestTemplates:
        application/json: !Sub |
          {
            "input": "$util.escapeJavaScript($input.json('$'))",
            "name": "$context.requestId",
            "stateMachineArn": "${pipelineMgrStateMachine}"
          }
      IntegrationResponses:
        - StatusCode: 200
    MethodResponses:
      - StatusCode: 200

pipelineMgrStageDeployer:
  Type: Custom::pipelineMgrStageDeployer
  DependsOn: webhookEndPointMethod
  Properties:
    ServiceToken: !GetAtt apiGwStageDeployer.Arn
    StageName: pipelinemgr
    RestApiId: !Ref pipelineMgrGW
<snip>

When I update the pipelineMgrStateMachine resource I see that the webhookEndPointMethod is updated even though nothing changes in the webhookEndPointMethod . As expected.

But, pipelineMgrStageDeployer is not updated. This is even the case when I make pipelineMgrStageDeployer dependent directtly on pipelineMgrStateMachine .

Any ideas on why the custom resource is not be updated when a resource it DependssOn is updated? Any other thoughts or insights that might be useful?

Thanks, Joe

Answer 1

There seems to be a misunderstanding on what DependsOn is for.

What's going on

From the CloudFormation DependsOn documentation

With the DependsOn attribute you can specify that the creation of a specific resource follows another. When you add a DependsOn attribute to a resource, that resource is created only after the creation of the resource specified in the DependsOn attribute.

The reason that your webhookEndPointMethod is likely updated when your pipelineMgrStateMachine is updated, is because it has an implicit dependency in your RequestTemplates

"stateMachineArn": "${pipelineMgrStateMachine}"

How can you make your custom resource get updated

As for how to have your deployer custom resource update when the state manager updates, you could add a property into your Custom resource that you don't actually use in it, like PipelineMgStateMachine: !Ref pipelineMgrStateMachine , for example:

pipelineMgrStageDeployer:
  Type: Custom::pipelineMgrStageDeployer
  DependsOn: webhookEndPointMethod
  Properties:
    ServiceToken: !GetAtt apiGwStageDeployer.Arn
    StageName: pipelinemgr
    RestApiId: !Ref pipelineMgrGW
    PipelineMgStateMachine: !Ref pipelineMgrStateMachine