Presigned-URL Uploads From a Serverless Function

The naive way to accept file uploads is to POST them to your API, let the server read the bytes, and write them to object storage. It works until the files get large or the traffic gets real. Now every upload crosses your infrastructure twice, once from the client to your server and once from your server to storage, and your server holds the whole file in memory or on disk while it does. On a serverless function it is worse, because functions have request-size and duration limits that a big upload runs straight into. Presigned URLs are the standard fix, and they predate serverless by a decade. Your server does not move the bytes; it hands the client a short-lived, pre-authorized URL and the client uploads directly to object storage. The server only issues permission and records metadata. On a Neon Function this is the same AWS S3 SDK you already use, pointed at the branch's storage endpoint. This post builds it and tests the whole round trip. The repo is at the end. TL;DR Proxying uploads through a function sends the bytes across it, burning bandwidth and memory and hitting request-size limits. A presigned URL is a time-limited, pre-authorized link to one object key. The client PUTs the bytes straight to storage; the function never touches them. On Neon Functions you generate it with getSignedUrl from @aws-sdk/s3-request-presigner , the same code as any S3-compatible store. I tested the full flow: presign, the client PUT straight to storage returned 200 , a metadata record was saved, and downloading the object returned the exact bytes. One gotcha to pin: the injected AWS_REGION is the storage-cell host, not a region, so set region: 'us-east-2' on the client. Prerequisites A Neon project on the platform preview with a declared bucket (object storage, us-east-2 ) The AWS SDK: @aws-sdk/client-s3 and @aws-sdk/s3-request-presigner Familiarity with S3-style object storage and HTTP PUT Why not just proxy the upload Sending the file through the function has three costs that