Bad Gateway The proxy server received an invalid response from an upstream server

[Santhosh Samban]

I am getting the following error, while accessing the site hosted in Microsoft Azure Virtual Server after waiting for few minutes.



502 Bad Gateway The proxy server received an invalid response from an upstream server.



**The most confusing part is that, if we refresh the page, it works perfectly fine and loads very fast**



The following is the configuration:

OS: Windows Server 2012, VC 14
    
    Webserver: Apache: 2.4.12
    
    Tomcat: 8.0.23
    
    Connector: Mod_JK 1.2.40

Apache workers conf:

worker.list=worker1
    worker.worker1.type=ajp13
    worker.worker1.host=localhost
    worker.worker1.port=8009

The following is the lines from the log file

 [Mon Jul 20 08:21:05 2015][2640:996] [info] ajp_connection_tcp_get_message::jk_ajp_common.c (1291): (w_tc) can't receive the response header message from tomcat, network problems or tomcat (xxx.xxx.xxx.xxx:8009) is down (errno=60)
    
    [Mon Jul 20 08:21:05 2015][2640:996] [error] ajp_get_reply::jk_ajp_common.c (2176): (w_tc) Tomcat is down or refused connection. No response has been sent to the client (yet)
    
    [Mon Jul 20 08:21:05 2015][2640:996] [info] ajp_service::jk_ajp_common.c (2673): (w_tc) sending request to tomcat failed (recoverable),  (attempt=1)

[Tim Holloway]

I think that there's 2 primary ways to get that message. One is when you're confusing SSL and non-SSL on the proxy channel.

The other would be what appears to be hurting you. It looks like the handshaking is failing due to timeouts.

Check the VM and Tomcat to ensure that you have enough memory allocated. If the VM paging rate is high, timeouts are a consequence.

You can also have timeouts if the VM itself is being starved of resources, but that's a lot harder to diagnose from an internal point of view.