"Service temporarily unavailable"

[Sandeep HS <hssandeep16@xxxxxxxxx>]

Hi ,

We have query related to Apache(httpd)-Tomcat communication and following
are the details.

*Our configuration:*
We have a web based tool where request to Tomcat service is send through
apache using proxy.
i.e., when some one selects a service on web page, apache acts as an
interface where it forwards the request to Tomcat and then send back
response from tomcat to web interface.

*Apache configuration:*
ProxyPass /reqheader/* https://localhost:PORT_X/reqheader/*
ProxyPassReverse /reqheader/* https://localhost:PORT_X/reqheader/*

Here PORT_X port is used by tomcat service.

*Query:*
When apache is trying to connect to backend server Tomcat at port PORT_X,
Sometimes that request fails and we get "Service temporarily unavailable"
message.

When "Service temporarily unavailable" issue is hit, we are seeing
following below message in error_log

[Mon Apr 20 14:45:06 2015] [error] (239)Connection refused: proxy: HTTPS:
attempt to connect to 127.0.0.1:PORT_X (localhost) failed
[Mon Apr 20 14:45:06 2015] [error] ap_proxy_connect_backend disabling
worker for (localhost)

By the error message it seems that whenever apache is trying to connect to
tomcat at port PORT_X and if there is no service running at this port then
this issue is hit.

I have tried to use retry=0 for PassProxy and it did not resolve the issue.
i.e,
ProxyPass /reqheader https://localhost:PORT_X/reqheader retry=0

*Below are my questions, can you please clarify*.
1. what can cause this issue?

2. How to identify exact root cause?

3. If this is known issue, is there any fix(configuration parameter or
patch ) available?

Also, please provide any reference documents for the same


Thanks,
Sandeep