Tomcat is an open-source web server and servlet container developed by the Apache Software Foundation, it was initially known as Jakarta Tomcat or Tomcat. If you want to deploy and execute Java applications that are written in Java technologies including Java Servlet, Java Server Pages (JSP), etc, then you require Tomcat. TomEE is built on top of Tomcat. It is the Java Enterprise Edition of Apache Tomcat (Tomcat + Java EE = TomEE).
If you have a website running on a production server with a Tomcat environment, your website might get thousands of web requests per minute. At this point, you most likely feel that the memory resources usage in one Tomcat JVM become overwhelmed. To prevent your server from going down or unresponsive, you can configure a Tomcat cluster by placing two or more Tomcat servers. A cluster is a group of servers that communicate with one another, and the Tomcat instance in a Tomcat cluster is often referred to as a node. Clustering instances of Tomcat make them interconnected.