The WSO2 Application Server has Apache Axis2 framework as its core and is distributed under Apache License 2.0. It has full support for Apache Tomcat, which is the underlying Web application container and can be installed standalone or on top of Tomcat, WebSphere, WebLogic, Jboss or as part of a Java EE compliant servlet container.

Because the WSO2 Application Server is part of WSO2 Carbon, the component-based middleware platform, it consists of a set of pluggable components. Developers have the choice to deploy only the required components and leave unwanted functionality which adds to the bulk.

The diagram below describes WSO2 Application Server architecture from a messaging perspective.

Messaging architecture in WSO2 AS

The diagram shows how a message propagates through a typical WSO2 Application Server implementation but the functionality is not limited to what is depicted here.

Different Web channels such as client applications or mobile phones, communicate with an enterprise's application server through the Internet or a private network. These Web channels typically use XML/SOAP or REST messages.
The "transport" in the message receiver’s end manages concurrent connections and listens to messages contacting the application server via a particular protocol. For example, an “HTTP transport listener” detects XML/SOAP messages communicated in the HTTP protocol.
A transport which detects a message identifies if it needs any additional processing, also known as Quality of Service (QoS) operations such as security checks. The transport then sends the message through a message pipe containing handlers to take care of the additional processing.
Once the message has gone through the message pipe, it is passed on to the Message Receiver.
The Message Receiver determines the Web Service that needs to be invoked out of the services deployed in the application server and executes it.

This is how a message sent from a Web channel communicates with the Application Server and invokes a Web Service. Similarly, Web Application clients can call Web applications deployed inside the Application Server directly through Tomcat transports (HTTP/S).

All these components can be managed and monitored through the WSO2 Application Server's Management Console.

Application server components

The following scheme visually presents the component-based architecture of the WSO2 Application Server.

Component-based architecture in WSO2 AS

The WSO2 Application Server is a light-weight, high-performant and integrated Web services middleware platform. For it's Web service related functionalities, it uses components from the Apache WS-* stack. Apache Axis2 is the heart of the WSO2 Application Server's SOAP processing engine. Other components like Rampart, Sandesha2, Neethi etc. provide the other WS-* capabilities.

Transports

The WSO2 Application Server supports a number of transports through which the clients can send requests. As listed in the figure above, HTTP/S, JMS, Mail, XMPP and TCP are the main transports that are supported. In addition to that, any transport can be easily plugged in using the APIs provided by Axis2. For more information, see Working with Transports.

Web Services

The WSO2 Application Server supports different types of services. A service's type depends on the way the service is developed. However, finally all services are deployed within the Axis2 engine and features are available for all service types. For more information, see the topic on services development and deployment.

Applications

In the standalone mode, the WSO2 Application Server runs on top of an embedded Tomcat instance. This is from where it inherits the Web application deployment capabilities. It also supports development and deployment of other types of applications, including JAX-WS and JAX-RS.

For more information, see Developing Applications and Deploying Applications.

Tools

The WSO2 Application Server comes with different kinds of tools for running, testing and monitoring services and applications.

Carbon Context

The WSO2 Application Server has an in-built registry/repository to store the configuration and configuration metadata. It provides the facility to use a remote repository as well.

The WSO2 Governance Registry is something the WSO2 Application Server inherits from the WSO2 Carbon platform, the component-based platform upon which all WSO2 products are built. WSO2 Governance Registry acts as the metadata repository for the deployed services. In addition to that, users can use it for governance features as well. For more information, see Working with the Registry.

In addition, the Application Server can be deployed on other Application servers (as a Webapp) like WebSphere, WebLogic and Jboss as well.