Attach functions to externally defined API Gateway?

[WhileLoop]

I would like to split my API across multiple SAM templates but have the functions attached to the same API Gateway. Currently when using the "RestApiId" property I get the following message: "RestApiId property of Api event must reference a valid resource in the same template."

[sanathkr]

How are you trying to do it? Using ImportValue? Can you post an example snippet?

[WhileLoop]

At first I tried putting the ID of the gateway directly. This failed with the above error.

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Resources:
  SamTest:
    Type: AWS::Serverless::Function
    Properties:
      Handler: handler.Handle
      Runtime: python2.7
      CodeUri: package.zip
      Timeout: 10
      MemorySize: 1024
      Events:
        MyTimeApi:
          Type: Api
          Properties:
            RestApiId: abcd123456
            Path: /TimeResource
            Method: POST

Then I tried using import value. This created the Lambda without attaching it to the gateway.

Transform: AWS::Serverless-2016-10-31
Resources:
  SamTest:
    Type: AWS::Serverless::Function
    Properties:
      Handler: handler.Handle
      Runtime: python2.7
      CodeUri: package.zip
      Timeout: 10
      MemorySize: 1024
      Events:
        MyTimeApi:
          Type: Api
          Properties:
            RestApiId: !ImportValue MyRestApi
            Path: /TimeResource
            Method: POST

[edwardgale]

@WhileLoop - did you find a solution to this? I'm having the same issue whereby the API Gateway is configured externally not using a SAM template however it seems that SAM requires the API Gateway to be configured in the same template file.

[WhileLoop]

@edwardgale No, I did not.

[sanathkr]

Unfortunately CloudFormation doesn't modify resources created outside of your stack. If you have two stacks, one with API Gateway and other with Lambda functions, then you can use Fn::ImportValue to pass the Lambda ARN to APIGW stack to add an integration there. You can't use SAM there unfortunately because SAM operates entirely within the context of one template.

I am closing this issue because unfortunately we can't do anything about it. Feel free to comment or re-open if you have more use cases for something similar.

[allinwonder]

@sanathkr I am working on an API that associates with at least 4 functions. Each of these functions is using safe deployment with different pre/post hook functions. This means totally I have 12 functions in one template and plus others resources. These make the template grow to more than 1000 lines
which is really ugly and very hard to digest. I want to be able to split the functions and their pre/post Hook functions into its own template, and then use ImportValue or Parameters to inject the function Arn in the APIGW template. Is there any technical blocker to have this feature?

[rmullins-convene]

@allinwonder
That's my same situation. Did you think of any solutions?
The best solution I can come up of so far involves a complex CI build process.

Also - are your 4 functions split across their own git repos?