By default Hazelcast treats each instance as a completely separate node and as such will use any combination of the cluster nodes to hold copies (either for ownership or backups). This instantly introduces a problem where we run multiple JVM instances on the same machine (either physical or virtual). In that any host or hardware level issues that affect one JVM, might affect multiple at the same time, putting data resilience at risk.

To avoid this, we can configure Hazelcast to assign partitions not to an individual node, but to a defined group of nodes. Typically these groups of nodes will be known to share a common external risk or need to balance any differences in available memory; this siloing of nodes is referred to as partition grouping. There are currently two ways to configure a partition group:

Firstly, there exists an automatic process that handles the case of having multiple JVM instances running on the same machine; this is detected by having different...