Record the response status, request content type, approximate size and the time of the failure. Use a harmless test file and confirm available disk or object-storage capacity.

1. Check whether the response comes from the reverse proxy or from the application. A proxy rejection may occur before Express writes any request log.

2. Match the request format with the correct parser. JSON body limits do not configure multipart file uploads handled by separate middleware.

3. Review the maintained upload middleware’s file-size, field-count and storage settings. Keep limits appropriate for the actual feature instead of accepting unbounded uploads.

4. Check temporary storage, account quota and permissions. A completed network upload can still fail when the app writes or processes the file.

5. Retest a small valid file, the intended maximum and an oversized file. Return a clear controlled error and clean up partial data.

Confirm normal uploads complete, oversized uploads are rejected predictably and abandoned temporary files do not accumulate. Verify private uploads remain protected.

If processing times out after transfer, separate upload acceptance from expensive processing and consider a queue. Raising every proxy and application timeout may hide a resource problem.

Use a harmless small file first, then a larger test file within the application's intended policy. Record whether the browser rejects it before sending, the proxy rejects the request or the Express handler receives it and reports an error.

Review limits in the application middleware, proxy and storage destination separately. Increasing one limit does not fix a lower limit elsewhere. A failed write can also be caused by permissions, capacity or a temporary directory, rather than request size.

What should successful upload validation include?

Confirm the intended file type, size and storage location, and verify that the uploaded file cannot execute as application code. A renamed executable is not safe merely because its extension resembles an image. Apply the application's supported content validation and access controls.

Do not test with confidential documents or publish full request bodies in logs. Send us the request size, response status, time and redacted error excerpt if the problem appears to involve the hosting route. Keep the application account's write access limited to its required paths rather than applying broad permissions to the entire website.

• Keeping temporary uploads from filling application storage
• Using a queue for slow exports and notifications
• Validating API input before using it in a database
• Running Express behind a trusted reverse proxy
• Using WebSocket connections on eligible hosting

• Express API request parsing
• Multer documentation