'provided' runtime is not a supported runtime

[koote]

HI AWS SAM CLI folks,
I am migrating Go lambda runtime from go1.x to provided.al2, hit this error, I am using SAM CLI v1.23.0, does it mean this version is too old doesn't have provided runtime support? Which version of SAM CLI started to support provided.al2 runtime?

error log:

 SAM CLI, version 1.23.0

 Building codeuri: /tmp/project/helloworld runtime: provided.al2 metadata: {'BuildMethod': 'go1.x'} functions: ['HelloFunction']
 'provided' runtime is not a supported runtime

 Build Failed
 Error: GoModulesBuilder:Validation - Binary validation failed for go, searched for go in following locations  : [] which did not satisfy constraints for runtime: provided. Do you have go for runtime: provided on your PATH?

My template.yml:

  HelloFunction:
    Type: AWS::Serverless::Function
    Metadata:
      BuildMethod: go1.x
    Properties:
      FunctionName: HelloFunction
      CodeUri: helloworld/
      Handler: bootstrap
      Runtime: provided.al2
     ....

Also I have another question, when upgrading to provided.al2 runtime, must I specify BuildMethod? What is difference between BuildMethod: go1.x and BuildMethod: makefile with a makefile explicitly calls go build? Thanks!

[koote]

I think I know the answer of my 2nd question.

When specifying BuildMethod: makefile,CustomMakeBuilder (https://github.com/aws/aws-lambda-builders/blob/master/aws_lambda_builders/workflows/custom_make/DESIGN.md) is used, by default it copies the content of CodeUri folder to a temp folder and runs make from there (thus each subfolder should has it own Makefile);
When specifying BuildMethod: go1.x, GoModulesBuilder (https://github.com/aws/aws-lambda-builders/tree/master/aws_lambda_builders/workflows/go_modules) is used, it doesn't copy source to temp folder, instead it directly runs go build in the CodeUri folder.

When a project has multiple Lambda functions reside in different sub-folders and reference packages in parent folder or other folders, using BuildMethod: go1.x would be better, BuildMethod: makefile will introduce go module related issues, because it doesn't copy dependencies reside in other folders, it only copies the content in CodeUri folder.

If you must use BuildMethod: makefile, use --build-in-source option to prevent CustomMakeBuilder:CopySource action, but this option is introduced in SAM CLI v1.104 so need to upgrade SAM CLI.

If you cannot upgrade SAM CLI easily (for example the SAM CLI is in CI/CD system), the workaround is:

1. Set the CodeUri to the project root folder for each Lambda function, so CustomMakeBuilder copies whole project folder to temp folder before making targets.
2. Update the Makefile in project root folder to include new build targets build-Logical-ID to build each Lambda function, no need to create Makefile in each Lambda's sub-folder.