Working with proxy plugin issues

Before we understand how to deal with the proxy plug-in we need to understand what these proxy plugin are, how are they different from web servers, where they are present, etc. Let’s try to discuss each of these in details.
Introduction to Proxy Plug-in: Proxy Plug-in are mainly used to re-direct the requests to the application server based on the configurations specified inside plug-in config file.
The advantages of using the proxy plug-in are as follows:
1)      Re-direction of requests
2)      Load Balancing of requests
3)      Serves the static data (using the proxy cache)
Please find the below pictorial representation of a dynamic application server architecture containing the Proxy plug-in:

fig (a): proxy plug-in inside the dynamic application server architecture
Following are the list of proxy servers supported by Oracle BEA:-
1)      IIS plug-in
2)      Apache plug-in
3)      Netscape/SunOne plug-in
As we can observe from the above pic, the proxy plug-in is always available inside the webservers.  (They are different reasons for this)
Working with Proxy Plug-in related issues:
Following are most of the common problems/issues seen while working with the proxy plug-ins:
1)      Uneven Load balancing of the HTTP requests
2)      Frequent or unexpected session failover
3)      Unexpected http status codes in HTTP responses like 400, 404, 500, 503, etc for which the diagnosing at the weblogic server didn’t gave any clue.
*Note: for most of these issues updating of your existing plug-in will resolve the issue.
Enable the following debug flags inside the proxy sever plug-in config files to get more information about the issue:
1)      Set Debug=”ALL” :  Enabling these debug flag will give more traces of the following information:
a)      Headers sent to and from client.
b)      Headers sent to and from WLS.
c)      Information and error messages
2) Set DebugConfigInfo=”ON”: Enabling this flag will help the plug-in to log the following information:
a)      Returns the config information and runtime statistics to the browser
b)      Responds to the request that contain the string _WebLogicBridgeConfig
c)      Append the string _WebLogicBridgeConfigPath at the end of the URL.
Following is the example on how to use _WebLogicBridgeConfig:- http://hostname:portNo/contextPath/servletPath/pathInfo_WebLogicBridgeConfig
Executing the above URL will give the output that contains the complete information about the proxy plug-in like number if requests handled, max response time, min response time, time out, etc
Note:  Enabling any of the above parameters would require a server restart.
After enabling the above debug flags the output would by default routed to the following files depending up on the OS we are using:
1)      UNIX( related OS): /tmp/wlproxy.log
2)      Windows (related OS): C:\TEMP\wlproxy.log
Depending up on the Web Server we are using the proxy plug-in file name could be any of these two:
1)      Apache HttpServer: httpd.conf file
2)      Iplanet/SunOne: obj.conf file
3)      Microsoft IIS: iisProxy.Ini