Server :: Communication Between Apache And Resin?

I was going to upgrade apache from version 1.3 to version 2.2.15 on a test server (and later on prod servers).. i prepared really good for it by reading upgrading information, changes from 1.x - 2.x, read module documentation to check if any of the used modules had any different syntax and if it was supported for this new version of apache. Later i finally installed apache, upgraded all the used modules to be apache 2 compatible and everything seemed to go smooth. I started apache and resin and everything looked fine, the syntax was OK and everything so i reported back that it was ready.. but i got a feedback that the people that were going to use the server only got a proxy error or service unavailable error when apache was trying to send requests back to the backend resin server.. and this is the problem. I could just have told you that this was the problem, but i find it to be much easier if you have a little background information first to explain how the problem aried.

A couple of other people and myself has done quite extensive troubleshooting on this, we troubleshooted apache, mod_caucho and resin by themselves to check if it was any problems with them.. we could only find that mod_caucho didnt seem to behave correly, the caucho-status page was displaying an empty list of requests and what would be proxied back.. we are running the same version of mod_caucho and resin to be sure it would be compatible with eachother and all the software is running in 64-bit, only a 64-bit CentOS 4.4 OS (yes, the OS is really old but because of complications we are not ready to upgrade it yet).

When we try to telnet to the port where resin is listening its open and resin returns an X when you hit enter (like it should and says in Caucho' official troubleshooting tips). We have tried installing apache 2.2.11 instead of 2.2.15 and other versions of both resin and mod_caucho. Other modules has also been tried like mod_proxy to send the requests back and also the rewrite module with the P flag.. although this was not the preferred way to do it we only wanted to see if it had any difference which it didnt.

So after several hours of troubleshooting we are still not able to find the cause of why we are getting a proxy error (http 502) when apache is trying to send a request back. We have checked all the logs for apache and resin, we have also compiled the mod_caucho module with the "--enable-debug" option to get more verbose information but we didnt get any additional information this way eventhough we should according to Caucho' official site.

We have looked into both the resin and apache config and tried both ways of configuring mod_caucho.. and nothing seems to change the result.. we only get a 502 proxy error. So since it didnt work i downgraded to apache 1.3 one day and that was fine.. then it was upgraded again to apache 2.x to try to find out what the problems were but again we didnt find this.. so i was going to downgrade it again, but this time on a different test server, but after downgrading i for some very weird reason got the same proxy error i had when using apache 2 which is beyond my comprehension.. i just cannot understand this.

- has anyone had any similar experiences with or without the same setup ?

- does anyone know about any solution to this of can provide any additional advice on what to do further? Yes, we want the functionality in apache 2 so we will not settle with apache 1.3.. one of the features being the new filters to be able to capture requests for pre and post processing before they hit other modules.