Different server & browser HTTP status codes

Question

I have a small python web application running on nginx with unicorn. The web application refresh it's page automatically every 1 minute.

Every day I see that around the same hour, the browser reports a 504 Gateway Time-out error and the application stops refreshing obviously.

I checked it with both chrome and firefox on two different client machines and two different server machines and found out it happens almost everyday on the same time (different time for each web server).

The weird thing is that looking at the web server access log I identify these calls and they are reported with 200 OK status code.

Could it be the the browser reports a different error code than the server due to connection issues? Any ideas how should I keep investigating it?

Answer 1

Yes - the server is able to serve the page ok so returns 200, but the client cannot finish the connection.

It could be a part of your infrastructure (firewall?) is choosing to update or something, although the odds of this happening at the exact same time of your request is slim unless it's a long running request or gateway outage.

Answer 2

We found out the indeed our server had a maintenance procedure which blocked the access to it. Although it finished the request after a while the browser "gave up" and returned a timeout error. Once the maintenance procedure was canceled - the issue was resolved.