A vital part of an application server is its web container. In the previous incarnations of WildFly (when it was named JBoss AS), the old container, JBoss Web Server (JWS—https://www.jboss.org/jbossweb/), that was based on a fork of Apache Tomcat (http://tomcat.apache.org/), acted as an embedded Java EE web container.

As of WildFly 8, JWS has been replaced by technologies from the Java-based web server, Undertow (http://undertow.io/). Similar to JWS/Tomcat, Undertow can act both as a web server and a Java EE web container. It can also run in embedded mode, just as it does in WildFly, as well as in standalone mode.

Undertow was initially designed for speed. It is lightweight and adaptable, allowing it to handle new features and advanced technologies such as the WebSockets API and HTTP Upgrades, which we will discuss further on. The Undertow project is relatively new but has already come far when it comes to its initial goals. As it matures further in areas such as documentation...