Server - Service - Engine - Host, Tomcat
Archive - Originally posted on "The Horse's Mouth" - 2008-12-14 06:17:22 - Graham EllisA Tomcat Server can run one or more Services. Each Service comprises a number of Connectors and an Engine, which contains one or more Hosts.
You connect to a Tomcat Server via an appropriate connector, which defines the port number, the protocol, and various other connection parameters, and within the Tomcat server information is generated for the particular host (domain) that you're serving.
Q: Why would you want multiple services?
A: So that you can use a single copy of Tomcat to serve different hosts in different ways.
The top diagram shows you a server with five connectors and a single service, accessing 3 hosts. Any of the five connectors can access any of the five hosts, so you've a total of fifteen different routes to the data.The lower diagram shows, again, 5 connectors and 3 hosts - but this time two of the connectors access a service who's engine looks after just one host, and the other three connectors access a second service that looks after two hosts. Result? Just ( 2 x 1 + 3 x 2) = 8 different routes to data.
Why might this be useful? Let's say that the single host with two connectors provided internet-accessible http and https services, and the other two hosts were accessible via ajp and http proxies, together wish a second http port for testing. And that's all you wanted - no crossovers, but also no need to run two complete Tomcats!