Running and debugging Go Lambda functions locally

Brian Mayer
Nagoya Foundation
Published in
6 min readJul 25, 2020

A solution without CLIs, Docker or big frameworks; just a binary, a debugger and simple configs. This article is also available on my blog.

Debugging locally a lambda function written in Go is not a trivial task, this article is my trial at this subject, it represents the result of a week of intense research and frustration pursuing a thing that should be trivial for any developer: running your code on your machine and attaching a debugger to it. This setup it great for development and essential for building high quality software, but even after days of effort I wasn’t able to properly step-through my code, so I gave up and decided to do thing the old way.

After trying various approaches with recommended tools like aws-sam-cli and the serverless-framework with no success, I ended up with a very simple setup that let me step-through my code, check values and dig into the function execution, with the real debugging, and it was adopted in the back-end team at my company. So here it goes.

The setup is basically the following:

  1. Build your lambda function with debugging symbols
  2. Run it and attach the debugger
  3. Make a RPC call to it using a client (included here)
  4. Follow the code execution on visual studio

Needed software

  • go package delve, install it running: go get
  • go package awslambdarpc, install running go get
  • I used visual studio code but it should work on other IDEs
  • And for convenience and speed, the file-picker VSCode extension

Make sure your $GOPATH/bin folder is in your PATH so that VSCode can find them.

Before we start

Just a little brief, a lambda function is basically a RPC (remote procedure call) server, and RPC servers work in a different way: they advertise methods that they have available, and clients call these methods passing its name and the arguments needed, if any. In a lambda function the function exposed is called Invoke() and it’s defined on the Function type, so the method called is…