This page dedicates to issues I encountered, solved, and lesson learned during working with AWS. This is just a summary. See other notes for details.

SAM (&SAM CLI)

• Cors (in SAM template 'AWS::Serverless::Api' resource properties): format is like "'example'" ("'*'"), don't forget the double then single quote. This is due to HTTP spec requires the value of Allow properties to be a quoted string. If get this wrong, CloudFormation will report "Invalid mapping expression specified: *" (ah, AWS messages are always mysterious and misleading!)
• Cors: Cors works by SAM transforms Swagger definition, therefore only inline swagger definition works. Use AWS::Include is ok, considered inline. However, use "DefinitionUri" does not work.
• Integrate Swagger: can do in two styles. (1) Use "DefinitionUri": can specify the swagger file in a relative path ("swagger.json"), and with "aws cloudformation package" command the resource will be uploaded and uri replaced here. However the problem with this approach is (1) Cors would not work, since this is not inline (the transformed cloudformation template still refer to the file instead of embed the content), and (2) the Fn::Sub with resource defined outside of the swagger would not work, then the swagger file cannot integrate resources defined outside. So what really works is (2) Use "DefinitionBody: 'Fn::Transform':... as in the SAM git project example. Downside of this method is that 'aws cloudformation package' does not yet pack 'AWS::Include' location, so the complete s3 url needs to be provided and file needs to be uploaded. Also the included file needs to be in JSON format.

# Resources

    VCLinkAPI:

        Type: 'AWS::Serverless::Api'

        Properties:

            StageName: stage

            Cors: "'*'"

            DefinitionBody:

                'Fn::Transform':

                    Name: 'AWS::Include'

                    Parameters:

                        Location:

                            Ref: VCLinkAPISwaggerLocation

• Integrate Swagger: "example" in model does not work.
• SAM CLI - only mock up Lambda environment, don't expect API & DynamoDB be created locally