You must configure application servers for high availability.
Follow the instructions for configuring WebSphere Application Server for Content Platform Engine, but set the JDBC parameters for the nodes by using the administrative console, not the individual servers.
Follow the instructions Guide for configuring WebLogic Server for Content Platform Engine.
Follow the instructions for configuring JBoss Application Server for Content Platform Engine, but use JBOSS_DIST/all as the base configuration file set instead of JBOSS_DIST/server.