Hi,
1. What is the maximum load the single instance of gateIn supports? I mean the number of concurrent requests supported by GateIn?
> Well, it definatly depends of the instance characteritics, I mean, it depends on hardware environement (or virtual hardware vram vcpu)
2. Is gateIn supports clustered environement?
> Yes, at gatein level. https://community.jboss.org/wiki/GateInClustering & http://docs.exoplatform.com/PLF35/index.jsp
3. Is there any server monitoring tool like Memory utilization, session management, each porrtal application memeory utilization as part of the out of the box.
> Yes, look at https://docs.jboss.org/author/display/GTNPORTAL35/Administration+and+Monitoring & http://docs.exoplatform.com/PLF35/index.jsp?topic=%2Forg.exoplatform.doc.35%2FGadgetUserguide.ManagementMOnitoringGadget.html
you can use other tools such as http://code.google.com/p/javamelody/ & you can also jmx connect your AS using jconsole, visualvm, or even cacti https://community.jboss.org/wiki/ConnectingJconsoleToJBossAS
4. How many documents can be accessed through users at a time? (no of document by no of users in 1 sec?)
5. CPU utilization under 1 lac users.
> As I said in 1. it depends on your hardware (or vhardware), node number etc...
hope it helps