Question
A customer or Provider staff member cannot log into POA Control Panel, the following error message is displayed in browser:

Service Unavailable. The corresponding service is not available at the moment, try it within 2-3 minutes.
Cause
There may be several reasons of the problem:

The maximum number of request processing threads to be created by the Apache Tomcat’s HTTPConnector has been exceeded. In this case the following entries may be found in the /var/log/catalina.out file on the POA User Interface (UI) server:

Oct 9, 2013 2:56:06 PM org.apache.tomcat.util.threads.ThreadPool logFull
SEVERE: All threads (200) are currently busy, waiting. Increase maxThreads (200) or check the servlet status
Linux does not have the separate threads per process limit, just a limit on the total number of processes on the system (threads are essentially just processes with a shared address space on Linux) which you can find using the following command:

# cat /proc/sys/kernel/threads-max
POA Task Manager works slowly due to many pending tasks and as a result requests from the UI server time out (Control Panel requests POA Task Manager to provide list of pending tasks for customer’s subscription(s) when logging into POA CP).
Resolution
1. Increase the number of threads in the system by the following command on the POA UI server:

# echo new_value > /proc/sys/kernel/threads-max

2. Upgrade to POA 5.5.