The HTTP 502 “Bad Gateway” response is generated when Apache web server does not receive a valid HTTP response from the upstream server, which in this case is your Tomcat web application.
Some reasons why this might happen:
- Tomcat may have crashed
- The web application did not respond in time and the request from Apache timed out
- The Tomcat threads are timing out
- A network device is blocking the request, perhaps as some sort of connection timeout or DoS attack prevention system
If the problem is related to timeout settings, you may be able to resolve it by investigating the following: