Proxy Error 502 : The proxy server received an invalid response from an upstream server

Question

We are building a mass mailing sending application in Java. Mail is being send by third party SMTP. After sending 400-500 mails tomcat6 service get stopped. Below is the err

Answer 1

The java application takes too long to respond(maybe due start-up/jvm being cold) thus you get the proxy error.

Proxy Error

The proxy server received an invalid response from an upstream server.
 The proxy server could not handle the request GET /lin/Campaignn.jsp.

As Albert Maclang said amending the http timeout configuration may fix the issue. I suspect the java application throws a 500+ error thus the apache gateway error too. You should look in the logs.