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For information about how clustering applies to CloudHub 2.0, see Clustering.

A cluster is a set of up to eight servers that act as a single deployment target and high-availability processing unit. Unlike in server groups, application instances in a cluster are aware of each other, share common information, and synchronize statuses. If one server fails, another server takes over processing applications. A cluster can run multiple applications.

Before creating a cluster, you must create the Mule runtime engine instances and add the Mule servers to Anypoint Runtime Manager.

Multicast vs Unicast Clusters

While configuring a cluster, specify either unicast or multicast options for identifying a node within the cluster:

  • Unicast:

    A unicast cluster requires that you configure the IP addresses of the nodes in the cluster. If a server has multiple interfaces, use the internal IP address that allows the node to communicate directly with other nodes. Clustering across different availability zones or regions can cause a cluster performance issue, as it relies on high speed connectivity. Putting all cluster nodes on one subnet or in the same availability zone reduces performance risks.

    Because Mule relies on the IP address to identify the server, IP addresses can’t be dynamically assigned using DHCP for servers on a unicast cluster. If a server is restarted and uses DHCP to get a new IP address, you must add the server to the cluster using its new IP address.

    The server status must be Running to be added to a unicast cluster.

  • Multicast:

    A multicast cluster comprises servers that automatically detect each other. Servers that are part of a multicast cluster must be on the same network segment.

    One advantage of multicast clusters is that the server status doesn’t need to be Running to configure it as a node in a cluster. Another is that you can add nodes to the cluster dynamically without restarting the cluster.

    Check with your network administrator to determine if multicast is allowed within your network, because many networks block multicast functionalities.