Possibility to get AWS::Serverless::RestApi passed a template variable to Template files with Functions only

[ashwgupt]

We have got a problem where the resource limit of CF is hit when transformed from our SAM Template file.

Given all our Lambdas are behind APIs and we want to maintain all APIs from Single API Gateway, and that we now have to split the SAM Template into multiples to make them independently deploy-able, is there a way that we define one template that has only AWS::Serverless::Api to build out API Gateway with given Swagger file, and then to pass its reference to other template files that will be deploying our AWS::Serverless::Functions.

We simply want to pass the reference of RestApiId to the template files as a CFN Parameter.

Is this possible at this moment? As the error on the attempt says otherwise - RestApiId must be a valid reference to an 'AWS::Serverless::Api' resource in same template, which is quite dis-heartening :-(

[honglu]

You can use CloudFormation export and import to pass the parameters from one stack to a different stack: https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/using-cfn-stack-exports.html

To deal with resource limit issue, CloudFormation recommends to use nested stacks: https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/using-cfn-nested-stacks.html

The caveat here is that nested stack does not support SAM. One way to get around that is to only define the non serverless resources in nested stacks and still leave the serverless resources in the top level SAM template.
Edit: Nested stacks are now supported, starting November 2018

[ashwgupt]

@honglu thanks for your reply.

We have been doing what you suggested above and now only serverless resources are left in the SAM when we hit the CF limit after transformation.

There were 3 options we came up with and tried but all failed:

1. Define API gateway as a separate SAM file, take export of created Gateway. Split Lambdas into multiple Lambda-only SAM files, with all of these taking already created API Gateway as input for their event.properties.RestApiId => That fails due to the limitation that SAM has i.e. the RestApiId must be a valid reference of serverless:api type resource in the same template file.
2. Define API gateway as a separate SAM file and create Role/Policies such that it is allowed to invoke required functions. Split Lambdas into multiple Lambda-only SAM files but without any Api type Event defined under it. That way we can create our Lambdas and API Gateway independent of each other and integrate using Swagger and arrange for permissions separately => That fails at SAM Local level, upon which we depend a lot for local run and testing, as that now doesn't know against what event a lambda should listen.
3. Define API gateway as a separate SAM file and create Role/Policies such that it is allowed to invoke required functions. Split Lambdas into multiple Lambda-only SAM files but without RestApiId property for event => That gets even worse as now every lambda creates a new Api Gateway for itself assuming that is what it's asked for.
   So at the end we are still blocked in that catch-22 situation due to variety of limits and limitations of SAM and CF.

So at the end we are still blocked in that catch-22 situation due to variety of limits and limitations of SAM and CF.

Is there any other way or ideas that can help us overcome it?

PS: However I also came across another issue - #335 that indicates the option-1 was working until a few days back, which is really interesting and worth watching progressing on that issue.

[lestephane]

Hi Folks, #149 seems to imply one cannot split the api resource from the function resources. This issue seems to imply it is indeed possible, without giving template examples. I would be forever grateful if someone who's managed to do this would post an actual example that works. Many thanks in advance.

[saratitan]

We managed to split them before, but no longer. It suddenly stopped working so we had to redo all of our stack structure which meant a downtime in production. See #335

[mjbuonaccorsi]

Does anyone know if this issue is dead? Or does anyone know if there is a way to use the aws lambda update-function-code CLI method to update the code and roll it out with checkpoints?

[dehli]

It would also be great if RestApiId could be of type AWS::ApiGateway::RestApi instead of just AWS::Serverless::Api. We're currently using CloudFormation and would like to dry up some code by slowly switching to SAM but this prevents us from doing that.

[keetonian]

Nested stacks are now supported in SAM, meaning you can nest resources in other stacks and use the outputs as values in the current stack.

[dehli]

Even though they are supported, when I created the AWS::Serverless::Api in a separate stack from an AWS::Serverless::Function I still got the above error (this was two days ago).