How Do I Upload AWS Lambda Code?

How Do I Upload AWS Lambda Code?

What Actually Happens When You Upload Code

When you send that ZIP file to Lambda, AWS unpacks it automatically into the /var/task directory where your function executes. The console handles most of this behind the scenes—it stashes your ZIP in an S3 bucket first, then makes it available to your function. Skip this step and Lambda will throw a “no code” error. Always double-check your ZIP contains every file and dependency, either in the root or in a subfolder that matches your runtime’s expectations.

Here’s How to Actually Do It

1. Zip everything up
   • On Linux or macOS: zip -r function.zip . (run this from your project’s root folder)
   • In Windows PowerShell: Compress-Archive -Path * -DestinationPath function.zip
   • Trim the fat with zip -r function.zip . -x "*.git*" "*.DS_Store" so your ZIP stays under 50 MB
2. Head to the Lambda console
   • Open https://console.aws.amazon.com/lambda
   • Check the region in the top-right dropdown—make sure it matches where you want to deploy
3. Pick your function
   • Scroll through the list and click the function you want to update (for example, “MyAnalyticsFunction”)
4. Upload and confirm
   • In the “Code source” tab, choose Upload from → .zip file
   • Select your freshly made function.zip and hit Open
   • Click Save in the top-right corner; wait for the green “Code updated successfully” banner

Upload Still Failing? Try These Fixes

Work through the simplest fixes first, then move on only if you still hit problems:

• Console chokes on big ZIPs
  • ZIP files over 50 MB usually fail when uploaded directly in the console. Upload to S3 first, then point Lambda to that S3 location under “Code source” → “Amazon S3 location”
• Deploy with the AWS CLI (v2)
  • Install AWS CLI v2 from the official docs
  • Run: aws lambda update-function-code --function-name MyFunction --zip-file fileb://function.zip
  • Use --image-uri if you’re using container images
• Forgot to bundle dependencies
  • If your code needs libraries like NumPy or pandas, create a Lambda layer
  • Package those dependencies in a folder such as python/lib/python3.12/site-packages, ZIP it, then upload it as a layer that matches your function’s runtime
• Handler file ends up in the wrong place
  • Lambda looks for your handler file (for example, lambda_function.py) either in the ZIP’s root or in a folder that matches the handler path (for example, src/lambda_function.py with handler src.lambda_function.handler)

Keep Upload Problems From Happening Again