How Do I Upload AWS Lambda Code?

Quick Fix

What's Happening

Before Lambda can execute anything, it needs your code packaged up in a ZIP. The console quietly handles the heavy lifting—uploading that ZIP to an S3 bucket, unpacking it, and keeping it ready to run when triggered. No ZIP? No code. And without code, your function can’t do a thing.

Step-by-Step Solution

1. Package your code
   • On Linux or macOS, run: zip -r function.zip .
   • In Windows PowerShell, use: Compress-Archive -Path * -DestinationPath function.zip
2. Head to the Lambda console
   • Open https://console.aws.amazon.com/lambda
   • Pick your region from the dropdown in the top-right corner.
3. Select your function
   • Scroll through the list and click the name of the function you want to update.
4. Upload the ZIP file
   • In the “Code source” section, click Upload from → .zip file.
   • Find and select your function.zip file.
5. Save your changes
   • Click Save in the top-right corner.
   • Wait for the green “Saved” banner to appear—it confirms everything went through.

If This Didn't Work

Start with the simplest solution and move down the list:

• Console upload timeout
  • Big ZIP files (over 50 MB) often time out in the console. They need to go through S3 first.
  • Upload your ZIP to S3, then paste the S3 object URL into Lambda’s “Code” → “Code source” → “Amazon S3 location” field. Hit Save and you’re done.
• Deploy via the AWS CLI
  • Install AWS CLI version 2, then run:

    aws lambda update-function-code \
      --function-name MyFunction \
      --zip-file fileb://function.zip

• Missing layers
  • If your code depends on extra libraries—like pandas—you’ll need a layer.
  1. Go to the Lambda console, open Layers, and click Create layer.
  2. Upload the layer ZIP (make sure it matches your Lambda runtime).
  3. Back in your function, click Layers → Add a layer and select the one you just created.

Prevention Tips

Tip	Action
Version control	Push your code to GitHub or GitLab and tag releases. Use git archive to auto-build ZIPs whenever you tag—no more manual packaging.
CI pipeline	Set up a GitHub Action that runs sam build after every push, then deploys with sam deploy. No more forgetting to update your function.
Environment parity	Test locally first using AWS SAM CLI. It spins up a local Lambda environment so you can catch ZIP packaging issues before they reach AWS.
Clean up old versions	Lambda never deletes old code. Head to the console or run a CLI command to remove unused versions—otherwise, you’ll hit the 75 GB storage limit faster than you’d expect.