Nginx converts 409 from upstream to 502

[sachin.shetty@gmail.com]

Hi,

Our request flow looks like this:

client --> nginx --> haproxy --> tomcat

Put requests with large bodies are used to upload files. Sometimes due to
some application logic, tomcat may reject an upload early and return 409,
tomcat does not drain the input stream, we do not want to read the input
stream and rather reject early.

When tomcat rejects a PUT request early with 409, tomcat access logs show
409. The haproxy fronting tomcats also log a 409 in access logs, but nginx
logs a 502 and sends a 502 to the clients. It looks like nginx does not like
that request is rejected and a 409 is sent without reading the full request
by the upstream. 

What can we do to make sure client receives the correct response code i.e.
409

Thanks
Sachin

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,286531,286531#msg-286531