API Gateway SAM specify HTTP GET: 500 Internal Server Error

Question

I always get a 500 Internal Server Error when I try to call my GET endpoint that I defined using SAM.

I am able to define a POST request that works. For the GET request it's showing me: Lambda invocation failed with status: 403 Execution failed due to configuration error:

I think something is wrong where I define my DefinitionBody of my API Gateway.

Globals:
  Api:
    Cors:
      AllowMethods: "'GET,POST,OPTIONS'"
      AllowHeaders: "'DNT,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Range'"
      AllowOrigin: "'*'"
Resources:
  getFunction:
    Type: 'AWS::Serverless::Function'
    Properties:
      ...
      Events:
        GetApi:
          Type: Api
          Properties:
            Path: /tips
            Method: GET
            RestApiId: !Ref MyApi
  MyApi:
    Type: AWS::Serverless::Api
    Properties:
      StageName: dev
      EndpointConfiguration: REGIONAL
      DefinitionBody:
        swagger: "2.0"
        info:
          title: "API"
        paths:
          /tips:
            get:
              x-amazon-apigateway-integration:
                uri:
                  Fn::Sub: arn:aws:apigateway:${AWS::Region}:lambda:path/2015-03-31/functions/${getFunction.Arn}/invocations
                responses: {}
                httpMethod: "POST"
                type: "aws_proxy"

I already tried changing httpMethod on the x-amazon-apigateway-integration to "GET" but that is not solving my problem.

In the AWS Lambda console I see that the Lambda and Api Gateway are linked, yet I am unable to invoke the Lambda through the API Gateway. I can execute my Lambda successfully with a Test Event in the Console. It's definitely something on the API Gateway side.

Can someone verify what I am doing wrong?

Answer 1

After further digging around I found that I had to implement the GETmethod of the /tips path like this:

        get:
          responses:
            '200':
              description: 200 response
              headers:
                Content-Type:
                  type: string
          produces:
          - application/json
          x-amazon-apigateway-integration:
            uri:
              Fn::Sub: "arn:aws:apigateway:${AWS::Region}:lambda:path/2015-03-31/functions/${getTipsFunction.Arn}/invocations"
            passthroughBehavior:  when_no_match
            responses:
              default:
                statusCode: 200
                responseParameters:
                  method.response.header.Content-Type: integration.response.header.content-type
            httpMethod: POST
            type: aws

This solves the problem.