17.2. Introduction
17.2.1. About High-Availability and Load Balancing Clusters
- Instances of the Application Server
- Web applications, when used in conjunction with the internal JBoss Web Server, Apache HTTP Server, Microsoft IIS, or Oracle iPlanet Web Server.
- Stateful, stateless, and entity Enterprise JavaBeans (EJBs)
- Single Sign On (SSO) Mechanisms
- Distributed cache
- HTTP sessions
- JMS services and Message-driven beans (MDBs)
jgroups and modcluster. The ha and full-ha profiles have these systems enabled. In JBoss EAP 6 these services start up and shut down on demand, but they will only start up if an application configured as distributable is deployed on the servers.
17.2.2. Components Which Can Benefit from High Availability
Several instances of JBoss EAP 6 (running as a standalone server) or a server group's members (running as part of a managed domain) can be configured to be highly available. This means that if one instance or member is stopped or disappears from the cluster, its work load is moved to a peer. The work load can be managed in such a way to provide load-balancing functionality as well, so that servers or server groups with more or better resources can take on a larger portion of the work load, or additional capacity can be added during times of high load.
The web server itself can be clustered for HA, using one of several compatible load balancing mechanisms. The most flexible is mod_cluster connector, which is tightly integrated with the JBoss EAP 6 container. Other choices include Apache mod_jk or mod_proxy connectors, or the ISAPI connector and NSAPI connector.
Deployed applications can be made highly-available because of the Java Enterprise Edition 6 (Java EE 6) specification. Stateless or stateful session EJBs can be clustered so that if the node which is involved in the work disappears, another node can take over, and in the case of stateful session beans, preserve the state.
17.2.3. Overview of HTTP Connectors
| Connector | Web server | Supported operating systems | Supported protocols | Adapts to deployment status | Supports sticky session |
|---|---|---|---|---|---|
| mod_cluster | httpd in JBoss Enterprise Web Server, httpd provided by operating system (Red Hat Enterprise Linux, Hewlett-Packard HP-UX) | Red Hat Enterprise Linux, Microsoft Windows Server, Oracle Solaris, Hewlett-Packard HP-UX | HTTP, HTTPS, AJP | Yes. Detects deployment and undeployment of applications and dynamically decides whether to direct client requests to a server based on whether the application is deployed on that server. | Yes |
| mod_jk | httpd in JBoss Enterprise Web Server, httpd provided by operating system (Red Hat Enterprise Linux, Hewlett-Packard HP-UX) | Red Hat Enterprise Linux, Microsoft Windows Server, Oracle Solaris, Hewlett-Packard HP-UX | AJP | No. Directs client requests to the container as long as the container is available, regardless of application status. | Yes |
| mod_proxy | httpd in JBoss Enterprise Web Server | Red Hat Enterprise Linux, Microsoft Windows Server, Oracle Solaris | HTTP, HTTPS, AJP | No. Directs client requests to the container as long as the container is available, regardless of application status. | Yes |
| ISAPI connector | Microsoft IIS | Microsoft Windows Server | AJP | No. Directs client requests to the container as long as the container is available, regardless of application status. | Yes |
| NSAPI connector | Oracle iPlanet Web Server | Oracle Solaris | AJP | No. Directs client requests to the container as long as the container is available, regardless of application status. | Yes |
Learn more about each HTTP Connector
17.2.4. Node types
A worker node, sometimes referred to as a node, is a JBoss EAP 6 server instance which accepts requests from one or more client-facing HTTP servers that act as a proxy. JBoss EAP 6 can accept HTTP, HTTPS and AJP requests from Apache HTTP Server, Microsoft IIS or Oracle iPlanet Web Server (formerly Netscape Web Server).
Cluster node is a specialization of the worker node. Such a cluster may be load-balancing, high-availability or both. In a load-balancing cluster, a central manager distributes work loads amongst its nodes equally, by some situation-specific measurement of equality. In a high-availability cluster, some nodes are actively doing work, and others are waiting to step in if one of the active nodes leaves the cluster.
Example 17.1. Apache HTTP Server with mod_cluster configured
