Wiring handler.py to Lambda via API Gateway

Next, we need to wire up our API endpoints to Lambda and our handler.py entry point. This wiring looks like this in a serverless.yml configuration file:

functions:
  HandleSession:
    handler: handler.session
    events:
      - http:
          path: session
          method: get
          cors: true
      - http:
          path: session
          method: post
          cors: true
  HandleSessionDetail:
    handler: handler.session_detail
    events:
      - http:
          path: session/{id}
          method: get
          cors: true
          request:
            parameters:
              paths:
                id: true
      - http:
          path: session/{id}
          method: delete
          cors: true
          request:
            parameters:
              paths:
                id: true

We define two Lambda functions that have different configuration options, HandleSession and HandleSessionDetail.

Under each function's name, there are multiple statements that control configuration. Look at both sections and you'll notice the handler: statement, which instructs Lambda what code to call when the Lambda function is executed. For both, we'll be running one of the Python functions in handler.py that we covered in the preceding code snippet.

But what calls these Lambda functions in the first place? The events: section is responsible for setting up invocation points and making the connection between a particular event and our Lambda function. Across the FaaS landscape, functions are invoked in response to an event. In the AWS landscape, the number of events that can trigger a Lambda function is quite large. In this scenario, we are configuring events to be HTTP endpoints with a particular path and HTTP method. API Gateway is the proxy that will provide us with unique HTTPS URLs, which get wired up to our Lambda functions according to our configuration. As you read through the configuration, our design and intent should be apparent. Again, there are a seemingly infinite number of ways to set up an API with these technologies and this example just scratches the surface to discuss the overall pattern.