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I understand that sometimes a client will show an HTTP request as returning a 0 status code when the request fails to connect, timesout, etc, but I have never seen a server logging 0 as what it is sending back to the client.

I am running a Rails 4.2, ruby 2.2.x API. I was analyzing our logs the other day and noticed that a non-trivial number of requests were being responded with an HTTP status code of 0 by our Rails API. I have been unable to figure out why.

In some cases, it appears the request never makes it to the rails app. I only see the log message which I believe is logged by rack as to the request path and status returned. In other cases, I can see one of the early log messages we log from our application controller.

Has anyone seen such a behavior? I am not sure how to debug further without beginning to modify the standard rack middlewares that rails provides. I am not able to reproduce the situation myself; I only see this sporadically in our logs.

A bit more about our stack:

I realize it would probably be impossible to answer what exactly is happening here, so I am hoping instead for suggestions on how best to troubleshoot this.

Found that this is an issue with our Rails logging setup. By correlating these logs to our nginx access logs, I can see that a 302 is actually being returned to the client. This was commonly happening when the CSRF protection failed.

It looks like this is caused by a lograge (gem) bug: https://github.com/roidrage/lograge/issues/67

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