Posted on

Clustering Oracle Weblogic


Adding server nodes to the cluster

In order to add Managed Servers to your cluster definition, select the Configuration | Server sub tab of your Cluster definition:

Click on the Add button. On the next page, select an existing server and add it as a member of the cluster. (If you need adding some more servers, the second option “Create a new server and add it to this cluster” is fit for this purpose)

Once done, click the Finish button. Repeat that process to add the remaining Managed servers to the cluster. If you are running in Production mode, activate changes in Change Control panel.

Configuring the clustering transport

WebLogic server instances in a cluster communicate with each another using two basic network technologies:

  • IP sockets, which are the conduits for peer-to-peer communication between clustered server instances.
  • IP unicast or multicast, which are used by server instances to broadcast availability of services and heartbeats that indicate continued availability.

Difference between Unicast and Multicast

Unicast packets are sent from host to host. The communication is from a single host to another host. There is one device transmitting a message destined for one receiver.

Multicast is a special protocol for use with IP packets. Multicast enables a single device to communicate with a specific set of hosts, not defined by any standard IP address and mask combination. This allows for communication that resembles a conference call. The speaker’s message isn’t broadcasted everywhere, but only to those in the conference call itself. A special set of addresses is used for multicast communication.

Note: Oracle recommends that you use Unicast for messaging within a cluster, leaving multicast for backward compatibility with previous versions.

As a matter of fact, IP multicast broadcasts messages to applications but it does not guarantee that messages are actually received. If an application’s local multicast buffer is full, new multicast messages cannot be written to the buffer and the application is not notified when messages are dropped. Because of this limitation, there’s a chance that you may occasionally miss messages that were broadcasted over IP multicast. If multicast is your only option, then choose an appropriate address.

The default multicast value used by WebLogic Server is but you are allowed to use an IP address in the range from to If you are running instances of JBoss EAP in your network, consider that this server uses the address as default multicast address.

Besides this, if you run several clusters on your network, you need to check that the combination of multicast address and port must be unique. If two clusters on a network use the same multicast address, they should use different ports.

Troubleshooting Multicast:

In order to solve multicast issues, Oracle WebLogic server ships with a multicast test tool which can show evidence of most common cluster issues:

The Syntax is:

java utils.MulticastTest –n name -a address [-p portnumber]    [-t timeout]   [-s send]

For example, if running the cluster on the default address:

java utils.MulticastTest –A