Mulesoft uses Hazelcast® in their High Availability Cluster. A cluster is a set of Mule instances that acts as a unit. In other words, a cluster is a virtual server composed of multiple nodes. The servers in a cluster communicate and share information through a distributed shared memory grid. This means that the data is replicated across memory in different physical machines. If a node becomes unavailable due to failure or planned downtime, another node in the cluster can assume the workload and continue to process existing events and messages.