CirrusGrid multicast and redirecting requests to each server with load balancer provides session replication between the pairs of server nodes. This guarantees session exchange between the nodes through the local net and eliminates the need of additional software or Memcached. With this approach you can use a big clustered app hosting.
This instruction shows the clustering technology used in CirrusGrid by the example of the Tomcat app server.

The given scheme presents a Tomcat cluster with two servers and one load balancer. All requests are handled and distributed by the balancer between different nodes due to the availability and server load.
If one of the servers fails, the users from that node will be automatically switched to the other instance of this Tomcat cluster. Thanks to the replication, the other instance already has all the sessions of the failed node, so end-users never notice any change.
To use the Tomcat clustering in Jelastic you have to come through the next steps:
1. Log into your CirrusGrid dashboard.
2. Click New Environment.

3. Pick Tomcat as the application server you want to use, specify the cloudlet limits and turn on High-availability as shown in the picture below. State the name of the environment and click Create.
