Unable to specify x-amazon-apigateway-integration uri with Sub function

Question

I have a swagger.yaml file with the following:

paths:
  /path/endpoint:
    post:
      ...
      x-amazon-apigateway-integration:
        uri: !Sub "arn:aws:apigateway:${AWS::Region}:lambda:path/2015-03-31/functions/${MyFunction.Arn}/invocations"

When I try to deploy this with the sam cli I get the error "AWS ARN for integration must contain path or action" in CloudFormation.

However, if I hardcode the AWS::Region value and MyFunction.Arn, I do not get the error.

Does anyone know why the Sub function is not working for the uri?

Answer 1

Yes, you need to format your integration path like this when using yaml format for the swagger yaml:

x-amazon-apigateway-integration:
    uri:
      Fn::Sub: "arn:aws:apigateway:${AWS::Region}:lambda:path/2015-03-31/functions/${MyFunction.Arn}/invocations"

The short form (for sub, "!Sub") which you are using will give you problems. You need to use the long form, Fn::Sub If you are working with SAM I also reccomend you review the AWS documentation on intrinsic functions, especially using Sub in conjuction with Imports. Hope this helps.

Answer 2

Shravan mentioned half of the problem. The other thing you need to do is use "DefinitionBody" and "Fn::Transform", as shown below, when adding your swagger file to your template or the variables in your swagger file will not be substituted.

Resources:
  MyApi:
    Type: AWS::Serverless::Api
    Properties:
      Name: my-api
      StageName: dev
      DefinitionBody:
        'Fn::Transform':
          Name: 'AWS::Include'
          Parameters:
            Location: s3://my-api/swagger.yaml

Simply using "DefinitionUri" to specify your swagger file will not work.

# This will cause the variables in your swagger file to not be substituted. You must use the format above to get variables to work in your swagger file.
Resources:
  MyApi:
    Type: AWS::Serverless::Api
    Properties:
      Name: my-api
      StageName: dev
      DefinitionUri: swagger.yaml

Unfortunately this also means you need to specify the full s3 path to your swagger file and upload it to S3 before deploying your SAM. See: https://github.com/awslabs/serverless-application-model/issues/305