Cluster Service - Red Hat CLUSTER SUITE FOR ENTERPRISE LINUX 4.6 Overview

High-availability service management provides the ability to create and manage high-availability
cluster services in a Red Hat cluster. The key component for high-availability service
management in a Red Hat cluster,
applications. In a Red Hat cluster, an application is configured with other cluster resources to
form a high-availability cluster 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
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 1.10, "Failover
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.
, implements cold failover for off-the-shelf
rgmanager
Domains", Failover Domain 1 is configured to restrict failover within that
High-availability Service Management
Figure 1.10, "Failover
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