How can I test AWS Lambda functions locally?

Question

Explain to me please what is the best way to locally test the lambda function. I used sam local and this solution https://github.com/lambci/docker-lambda for testin

Answer 1

This is how I test local lambda functions without Serverless frameworks, I run an HTTP post on local (quite easy setup for Go)

• decouple lambda logic like so:

func HandleRequest(ctx context.Context, request events.APIGatewayProxyRequest) (events.APIGatewayProxyResponse, error) {
    _, _ = pretty.Println("parsed:", request.Body)
    return events.APIGatewayProxyResponse{Body: "response is working", StatusCode: 200}, nil
}

• main function then checks if it is a local instance then run local post endpoint, else start lambda

func main() {
    environment := loadEnv()
    if environment == "develop" {
        router.NewRouter()
        select {}
    } else {
        lambda.Start(lambdahandler.HandleRequest)
    }
}

• in between you have an Adapter Pattern that converts your http request to whatever your lambda function accepts, for example:

func MapToApiGateway(w http.ResponseWriter, r *http.Request) (interface{}, error) {
    request := new(EmailResponderRequest)
    if err := json.NewDecoder(r.Body).Decode(request); err != nil {
        return err.Error(), err
    }
    apiGatewayRequest := mapHttpRequestToGatewayRequest(*request)
    events, err := lambdahandler.HandleRequest(nil, apiGatewayRequest)
    if err != nil {
        return err.Error(), err
    }
    return events, nil
}