431 Request Header Fields Too Large

I tend to get a 431 Request Header Fields Too Large error with express when running serverless offline start (serverless-offline plugin). Deleting event.multiValueHeaders fixes it, but it might break other things, I need to do more research:

exports.handler = (event, context) => {
    delete event.multiValueHeaders;
    return awsServerlessExpress.proxy(server, event, context)
}

The project where I’m having this issue is also using serverless-typescript though. This issue was very annoying to find so therefor sorry for lack of other information, I’ll try to update this issue if I find out more.

[kennyhyun]

http.maxHeaderSize can be overridden by max-http-header-size (nodejs >12.6, >10.15) https://nodejs.org/api/cli.html#cli_max_http_header_size_size (16KB on nodejs 14 by default)

in package.json

  "start": "node --max-http-header-size=16384 server.js",

[larrybolt]

@georgeevans1995 the solution initially suggested, delete event.multiValueHeaders; before passing the event to awsServerlessExpress.proxy seems to work for us.