AWS Lambda: Response payload size exceeded maximum allowed payload size
Synchronous invocations have a fixed 6 MB limit on the response (and on the request), and it cannot be raised. Your code ran to completion: the error is raised after the handler returns, which is why the function logs look clean. Behind API Gateway the practical limit is lower still, because binary bodies are base64 encoded and grow by a third, so anything over about 4.5 MB of file data will not fit. Large results have to leave the function another way.
Quick fix
Read the commands before running them. Anything that restarts a service, deletes data or changes permissions should be tried on a non-production system first.
# How big is the response? Log it just before returning
# console.log('response bytes', Buffer.byteLength(JSON.stringify(result)))
# Large files: write them to S3 and return a short-lived link instead
aws s3 cp report.pdf s3://my-bucket/reports/report.pdf
aws s3 presign s3://my-bucket/reports/report.pdf --expires-in 900
# ...then return {"statusCode": 302, "headers": {"Location": "<presigned url>"}}
# Large JSON: paginate, or gzip it when the client accepts that
# (return isBase64Encoded: true with a Content-Encoding: gzip header)
# Function URLs can stream responses past the buffered 6 MB limit
# (Node.js handlers wrapped in awslambda.streamifyResponse)
aws lambda update-function-url-config --function-name my-func --invoke-mode RESPONSE_STREAMHow to diagnose Serverless errors
Serverless errors are shaped by hard platform limits: execution duration, deployment package size, memory, and concurrency. Unlike a server you control, these cannot be tuned away. The fix is to restructure the workload. VPC-attached functions add a second class of problem, because they lose default internet access and depend on ENI capacity and NAT configuration.
If the quick fix above does not resolve it, work through these steps. They apply to this whole class of error, not just to this one message, which is usually what saves the time.
- Check the platform limit before changing code: timeout, package size and memory are all documented, and the error is usually the limit being reported literally.
- For timeouts, add timing logs around each external call. A function that times out is nearly always waiting on one downstream dependency.
- Reduce package size with layers, tree-shaking, and by excluding dev dependencies and the provider SDK that the runtime already includes.
- For VPC functions with no internet access, confirm there is a NAT Gateway or the relevant VPC endpoints. A function in a private subnet cannot reach the public internet by default.
- Measure cold start separately from warm invocation in your metrics, and use provisioned concurrency only after confirming cold starts are the actual problem.
Tools worth reaching for
CloudWatch Logs Insightsaws lambda get-function-configurationX-Ray / distributed tracingsam local invoke
Authoritative references
Primary documentation for this error, worth reading before applying any fix in production.
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Something missing or wrong?
This entry is maintained by hand. If the fix is out of date, incomplete, or you have a better one, email a correction and it will be reviewed.