Python -- ConnectionError: Max retries exceeded

Question

I occasionally get this error when my server (call it Server A) makes requests to a resource on another one of my servers (all it Server B):

ConnectionError: HTTPConnectionPool(host='some_ip', port=some_port): Max retries exceeded with url: /some_url/ (Caused by : [Errno 111] Connection refused)

The message in the exception is
message : None: Max retries exceeded with url: /some_url/ (Caused by redirect)
which I include because it has that extra piece of information (caused by redirect).

As I said, I control both servers involved in this request, so I can make changes to either and/or both. Also, the error appears to be intermittent, in that it doesn't happen every time.

Potentially relevant information -- Server A is a Python server running apache, and Server B is a NodeJS server. I am not exactly a web server wizard, so beyond that, I'm not exactly sure what information would be relevant.

Does anyone know exactly what this error means, or how to go about investigating a fix? Or, does anyone know which server is likely to be the problem, the one making the request, or the one receiving it?

Edit: The error has begun happening with our calls to external web resources also.

Answer 1

You are getting a CONN Refused on "some_ip" and port. That's likely caused by - No server actually listening on that port/IP combination - Firewall settings that send Conn Refused (less likely a cause!) - Third - a misconfigured (more likely) or busy server, that cannot handle requests.

I Believe When - server A is trying to connect to server B you are getting that error. (Assuming it's Linux and/or some unix derivative) what does netstat -ln -tcp show on the server? (man netstat to understand the flags - what we are doing here is - trying to find which all programs are listening on which port). If that indeed shows your server B listening - iptables -L -n to show the firewall rules. If nothing's wrong there - it's a bad configuration of listen queue most probably. (http://www.linuxjournal.com/files/linuxjournal.com/linuxjournal/articles/023/2333/2333s2.html) or google for listen backlog.

This most likely is a bad configuration issue on your server B. (Note: a redirect loop as someone mentioned above - not handled correctly could just end up making the server busy! so possibly solving that could solve your problem as well)