/debug-lambda-vscode

Debugging AWS Lambda with VSCode

Here the resources to the webinar.

Prerequisites

These are the things needed to set up a AWS SAM project for local debugging.

Setup

The project is set up with the help of the AWS SAM CLI.

sam init

This command will create an AWS SAM project with a basic hello-world function that uses the Node.js v10 runtime. The project will be created inside a new sam-app directory.

Run Lambda Locally

The AWS SAM CLI allows us to run a AWS Lambda function locally inside a Docker container.

Without Debugger

A basic execution can be done with the following command:

sam local invoke -e event.json HelloWorldFunction

With Debugger

A debug execution can be done with the following command:

sam local invoke -d 9999 -e event.json HelloWorldFunction

The port here has to be the same as in the launch.json

VSCode launch.json Configurations

The configurations used inside the launch.json

Basic Debug

The basic launch config will connect to an already running AWS SAM CLI process. So SAM CLI has to be run manually first.

{
  "name": "Attach to SAM CLI",
  "type": "node",
  "request": "attach",
  "address": "localhost",
  "port": 9999,
  "localRoot": "${fileDirname}",
  "remoteRoot": "/var/task",
  "protocol": "inspector",
  "stopOnEntry": false
}

VSCode Integration Debug

This config allows a one-click experience, but has to be created for every function/event combination. VSCode will start the SAM CLI by itself.

{
  "name": "Debug with event.json",
  "type": "node",
  "request": "launch",
  "runtimeExecutable": "sam",
  "runtimeArgs": [
    "local",
    "invoke",
    "-d",
    "9999",
    "-t",
    "${workspaceRoot}/template.yaml",
    "-e",
    "${workspaceRoot}/events/event.json",
    "${selectedText}"
  ],
  "port": 9999,
  "localRoot": "${fileDirname}",
  "remoteRoot": "/var/task",
  "protocol": "inspector",
  "stopOnEntry": false
}

Advanced VSCode Integration Debug

This will pass the selected text, which should contain of function name and a event name, to a special shell script. This script will, in turn, pass it to the SAM CLI as arguments. This lets VSCode start SAM CLI and allows for one launch config for multiple events and functions.

The launch.json config looks like this:

{
  "name": "Debug with script",
  "type": "node",
  "request": "launch",
  "runtimeExecutable": "${workspaceRoot}/debug.sh",
  "runtimeArgs": ["${selectedText}"],
  "port": 9999,
  "localRoot": "${fileDirname}",
  "remoteRoot": "/var/task",
  "protocol": "inspector",
  "stopOnEntry": false
}

It will pass the selectedText as an argument to the debug.sh

The debug.sh looks like this:

#!/bin/bash
IFS=' ' read -r -a array <<< "$1"

sam local invoke -d 9999 \
-t "./template.yaml"
-e "./events/${array[1]}.json" \
${array[0]}

NOTE: Don't forget to set execution permissions for the debug.sh! :D

It will split the selectedText argument and use the first part as the function name and the second part as the event name.

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