Installation guide

service. A high-availability cluster service can fail over from one cluster node to another with no

apparent interruption to cluster clients. Cluster-service failover can occur if a cluster node fails or if a

cluster system administrator moves the service from one cluster node to another (for example, for a

planned outage of a cluster node).

To create a high-availability service, you must configure it in the cluster configuration file. A cluster

service comprises cluster resources. Cluster resources are building blocks that you create and

manage in the cluster configuration file — for example, an IP address, an application initialization

script, or a Red Hat GFS shared partition.

You can associate a cluster service with a failover domain. A failover domain is a subset of cluster

nodes that are eligible to run a particular cluster service (refer to Figure 1.9, “ Failover Domains” ).

Note

Failover domains are not required for operation.

A cluster service can run on only one cluster node at a time to maintain data integrity. You can

specify failover priority in a failover domain. Specifying failover priority consists of assigning a

priority level to each node in a failover domain. The priority level determines the failover order —

determining which node that a cluster service should fail over to. If you do not specify failover

priority, a cluster service can fail over to any node in its failover domain. Also, you can specify if a

cluster service is restricted to run only on nodes of its associated failover domain. (When associated

with an unrestricted failover domain, a cluster service can start on any cluster node in the event no

member of the failover domain is available.)

In Figure 1.9, “ Failover Domains” , Failover Domain 1 is configured to restrict failover within that

domain; therefore, Cluster Service X can only fail over between Node A and Node B. Failover Domain

2 is also configured to restrict failover with its domain; additionally, it is configured for failover

priority. Failover Domain 2 priority is configured with Node C as priority 1, Node B as priority 2, and

Node D as priority 3. If Node C fails, Cluster Service Y fails over to Node B next. If it cannot fail over to

Node B, it tries failing over to Node D. Failover Domain 3 is configured with no priority and no

restrictions. If the node that Cluster Service Z is running on fails, Cluster Service Z tries failing over to

one of the nodes in Failover Domain 3. However, if none of those nodes is available, Cluster Service

Z can fail over to any node in the cluster.

⁠Chapt er 1 . Red Hat Clust er Suit e Overview