Kindly enable the access logger of Tomcat of the product. This can be done by modifying the <MASTER_prod_home>/conf/server.xml file. Have a BACKUP of this file by creating a COPY of it before doing any modifications.
1) Search for "access log" string in that file
2) After the "-->" string occurring after "access log", insert the following:
<Valve className="org.apache.catalina.valves.AccessLogValve" directory="logs" pattern="%t %u %U %{JSESSIONIDSSO}c "%{Referer}i" %a %A %m %D %b %s %r "%{User-Agent}i"" prefix="localhost_access_log." resolveHosts="false" suffix=".log"/>
3) Save and close the file
4) Restart the server
Shut down the MASTER.
After this re-name the existing Slave setup's folder name and try to create a new mirror setup.
Have attached a web.xml file with this ticket. Replace it with the file in <MASTER_prod_home>fos/WEB-INF. Before replacing, kindly create a BACKUP COPY of that file.
Start the MASTER now.
A new mirror setup (Slave) will be created now and certain configuration changes have been made to test whether everything works fine.
Upon the FOS service failing next time, kindly ask the the whole log folder of the Master, the fos log of the Master and the fos log of the Slave.