vscode-recipes/debugging-lambda-functions

Debugging AWS Lambda functions with SST

by Jay V (@jayair)

SST is a framework for building serverless applications. It allows you to test and debug your Lambda functions locally without having to redeploy your changes. It does this by streaming the Lambda function requests from AWS to your local client and running it locally. So for Node.js Lambda functions, you can set breakpoints locally and they'll reflect the event and context of the deployed Lambda function.

This guide will help you configure VS Code to support setting breakpoints and debugging your Lambda functions.

Getting started

Requirements

1. The latest version of VS Code installed.
2. A project initialized with the SST CLI.

Configure launch.json file

1. Open your project folder in VS Code.

2. Click on the Debug icon in the Activity Bar to switch to the Debug view.

3. Under Run and Debug click on create a launch.json file.

4. In the Select environment input, select Node.js.

   

5. Replace the content of the generated launch.json file with the following configuration:

   {
     "version": "0.2.0",
     "configurations": [
       {
         "name": "Debug SST Start",
         "type": "node",
         "request": "launch",
         "runtimeExecutable": "${workspaceRoot}/node_modules/.bin/sst",
         "runtimeArgs": ["start", "--increase-timeout"],
         "console": "integratedTerminal",
         "skipFiles": ["<node_internals>/**"]
       },
       {
         "name": "Debug SST Tests",
         "type": "node",
         "request": "launch",
         "runtimeExecutable": "${workspaceRoot}/node_modules/.bin/sst",
         "args": ["test", "--runInBand", "--no-cache", "--watchAll=false"],
         "cwd": "${workspaceRoot}",
         "protocol": "inspector",
         "console": "integratedTerminal",
         "internalConsoleOptions": "neverOpen",
         "env": { "CI": "true" },
         "disableOptimisticBPs": true
       }
     ]
   }
   

This JSON file defines two configurations, one for the sst start command; to debug your Lambda functions. And another for the sst test command; to debug your tests.

Debugging your Lambda functions

SST runs your Lambda functions locally and streams the requests back to AWS. So your functions can be debugged like any other Node.js application.

1. Open a Lambda function inside the src/ directory.
2. Put a breakpoint 🔴 anywhere in the function.
3. Switch to the Debug view and select "Debug SST Start".
4. Press F5 or click on Start debugging.
5. Tadaa! 🎉 Your breakpoint should be hit, and now you have full access to the event and context of the deployed Lambda function.

Additional resources

• Live Lambda Development
• How to debug Lambda functions with Visual Studio Code