Apache Tomcat 8 Architecture

In the Tomcat world, a Server represents the whole container. Tomcat provides a default implementation of the Server interface which is rarely customized by users.

A Service is an intermediate component which lives inside a Server and ties one or more Connectors to exactly one Engine. The Service element is rarely customized by users, as the default implementation is simple and sufficient: Service interface.

An Engine represents request processing pipeline for a specific Service. As a Service may have multiple Connectors, the Engine receives and processes all requests from these connectors, handing the response back to the appropriate connector for transmission to the client. The Engine interface may be implemented to supply custom Engines, though this is uncommon.

Note that the Engine may be used for Tomcat server clustering via the jvmRoute parameter. Read the Clustering documentation for more information.

A Host is an association of a network name, e.g. www.yourcompany.com, to the Tomcat server. An Engine may contain multiple hosts, and the Host element also supports network aliases such as yourcompany.com and abc.yourcompany.com. Users rarely create custom Hosts because the StandardHost implementation provides significant additional functionality.

A Connector handles communications with the client. There are multiple connectors available with Tomcat. These include the HTTP connector which is used for most HTTP traffic, especially when running Tomcat as a standalone server, and the AJP connector which implements the AJP protocol used when connecting Tomcat to a web server such as Apache HTTPD server. Creating a customized connector is a significant effort.

A Context represents a web application. A Host may contain multiple contexts, each with a unique path. The Context interface may be implemented to create custom Contexts, but this is rarely the case because the StandardContext provides significant additional functionality.