如何从API网关将请求类型传递给lambda？

Question

I have a lambda working from API gateway at the moment. but it's just hardcoded to GET data. I want to post some data via gateway & lambda to RDS. I want to do it in the same lambda and use some conditional blocks or switch statement inside it.

Is there any way to tell lambda what the request type is (GET/POST etc) and then the payload with it so that the lambda correctly routes and only executes that particular part of the function?

something like:

    exports.handler = (event, context, callback) => {
        context.callbackWaitsForEmptyEventLoop = false
        pool.getConnection(function(err, connection) {
          if (err) callback(err)

          if (request === GET && payload === exercises) {
             connection.query('SELECT * FROM exercises', function (error, results, fields) {
          } else if (request === POST && payload === workouts){
         // do some INSERT INTO sql statement
}


            connection.release();

            if (error) callback(error)
            else callback(null, results)

          });
        })
    }

Answer 1

This seems like a bad idea to begin with. You need to attach lambda function to a specific resource in your API Gateway (POST, GET method). When GET request comes to your API Gateway, API Gateway executes lambda function associated to that specific resource and the same goes for the POST request. Therefore you don't need to handle routing inside of your lambda function as it is handled by API Gateway. You just need to attach correct lambda function to correct resource in your API Gateway.

The only reason why you might need such functionality is that you are trying to attach the same lambda function to multiple resources which is a bad idea for more than just one reason. Such function will be more complicated than necessary (harder to maintain and debug), as well as it will run longer (though probably not by much in this case) which will result in increased costs.

So the solution is simply create one function that will handle GET request and one that will handle POST request.

Considering payload, you can access it via event parameter.

Answer 2

This is definitely possible with Lambda proxy integration , when you connect each resource method with the same Lambda:

exports.handler = async (event) => {
    if ('POST' === event.httpMethod) {
        ...
    }
    if ('GET' === event.httpMethod) {
        ...
    }
}

And it's probably fine for the beginning, when you don't have enough knowledge yet how to cut your domain into functions (sometimes called nanoservices , as building blocks of microservices), but generally it's considered to be a bad design due to maintainability - you're service is doing too much and the code becomes too conditional and therefore complex.

You can start with one Lambda and after domain boundaries are found, cut the logic into separated components, one per API resource, by its responsibility.