Overview

With RMI-IIOP load balancing, IIOP client requests are distributed to different server instances or name servers. The goal is to spread the load evenly across the cluster, thus providing scalability. IIOP load balancing combined with EJB clustering and availability also provides EJB failover.

When a client performs a JNDI lookup for an object, the Naming Service creates a InitialContext (IC) object associated with a particular server instance. From then on, all lookup requests made using that IC object are sent to the same server instance. All EJBHome objects looked up with that InitialContext are hosted on the same target server. Any bean references obtained henceforth are also created on the same target host. This effectively provides load balancing, since all clients randomize the list of live target servers when creating InitialContext objects. If the target server instance goes down, the lookup or EJB method invocation will failover to another server instance.

IIOP load balancing and failover happens transparently. No special steps are needed during application deployment. IIOP load balancing and failover for the Application Server supports dynamically reconfigured clusters. If the Application Server instance on which the application client is deployed participates in a cluster, the Application Server finds all currently active IIOP endpoints in the cluster automatically. Therefore, you are not required to manually update the list of endpoints if a new instance is added to the cluster or deleted from the cluster. However, a client should have at least two endpoints specified for bootstrapping purposes, in case one of the endpoints has failed.

Requirements

Sun Java System Application Server provides high availability of remote EJB references and NameService objects over RMI-IIOP, provided all the following apply:

• Your deployment has a cluster of at least two application server instances.

• Java EE applications are deployed to all application server instances and clusters that participate in load balancing.

• RMI-IIOP client applications are enabled for load balancing.

Application Server supports load balancing for Java applications executing in the Application Client Container (ACC). See Setting up RMI-IIOP Load Balancing and Failover.

Application Server does not support RMI-IIOP load balancing and failover over secure sockets layer (SSL).

Algorithm

Application Server uses a randomization and round-robin algorithm for RMI-IIOP load balancing and failover.

When an RMI-IIOP client first creates a new InitialContext object, the list of available Application Server IIOP endpoints is randomized for that client. For that InitialContext object, the load balancer directs lookup requests and other InitialContext operations to the first endpoint on the randomized list. If the first endpoint is not available then the second endpoint in the list is used, and so on.

Each time the client subsequently creates a new InitialContext object, the endpoint list is rotated so that a different IIOP endpoint is used for InitialContext operations.

When you obtain or create beans from references obtained by an InitialContext object, those beans are created on the Application Server instance serving the IIOP endpoint assigned to the InitialContext object. The references to those beans contain the IIOP endpoint addresses of all Application Server instances in the cluster.

The primary endpoint is the bean endpoint corresponding to the InitialContext endpoint used to look up or create the bean. The other IIOP endpoints in the cluster are designated as alternate endpoints. If the bean's primary endpoint becomes unavailable, further requests on that bean fail over to one of the alternate endpoints.

You can configure RMI-IIOP load balancing and failover to work with applications running in the ACC.