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242 Chapter 32. Clustering with JOnAS
Figure 32-4. Load Balancing
32.4.1. CMI Principles
CMI is a new ORB used by JOnAS to provide clustering for load balancing and high availability.
Several instances of JOnAS can be started together in a cluster to share their EJBs. It is possible
to start the same EJB on each JOnAS, or to distribute their load. A URL referencing several JOnAS
instances can be provided to the clients. At lookup time, a client randomly chooses one of the available
servers to request the required bean. Each JOnAS instance has the knowledge (through JavaGroups) of
the distribution of the beans in the cluster. An answer to a lookup is a special clustered stub, containing
stubs to each instance known in the cluster. Each method call on the home of the bean can be issued
by the stub to a new instance, to balance the load on the cluster. The default algorithm used for load
distribution is currently a weighted round-robin.
32.4.2. CMI Configuration
•
In the
build.properties
of the application, set the protocol name to
cmi
before compilation:
protocols.names=cmi
•
In the file
carol.properties
of the directory
$JONAS_BASE/conf
), set the protocol to
cmi
:
carol.protocols=cmi
•
In the file
carol.properties
, configure the multicast address, the group name, the round-robin
weighted factor, etc. For example:
# java.naming.provider.url property
carol.cmi.url=cmi://localhost:2002