In the above figure, the salespkg is running on the New York cluster and can be recovered by the Los Angeles cluster. Similarly, the custpkg running on the Los Angeles cluster can be recovered by the New York cluster. As stated previously, physical data replication is carried out using ESCON (Enterprise Storage Connect) links between the disk array hardware in New York and Los Angeles via an ESCON/WAN converter at each end. Each cluster is running a monitor that checks the status of the alternate cluster.
As depicted in the above example, each cluster runs just like any Serviceguard cluster, with applications configured in packages that may fail from node to node as necessary. Each cluster is configured with a recovery version of the packages that are running on the alternate cluster. These packages do not run under normal circumstances, but are set to start up when they are needed. In addition, either cluster may run other packages that are not involved in Continentalclusters operation.
Application Recovery in Continentalclusters
If a given cluster in a recovery pair of cluster should become unavailable, Continentalclusters allows an administrator to issue a single command, cmrecovercl (described later) to transfer mission critical applications from that cluster to another cluster, making sure that the packages do not run on both clusters at the same time. Transfer is not automatic, although it is automated through a recovery command, which a root user must issue. The result after issuing the recovery command is shown in Figure 13.
Figure 13 Continentalclusters After Recovery
The movement of an application from one cluster to another cluster does not replace local failover activity; packages are normally configured to fail over from node to node as they would on any high availability cluster. Cluster recovery, failover of packages to a different cluster, occurs only after the following events:
•Continentalclusters detects the problem
•Continentalclusters sends a notification of the problem
•Verify that the monitored cluster has failed
•Issue the cluster recovery command
Understanding Continentalclusters Concepts 39