Red Hat ENTERPRISE LINUX 4 Manual

Also see for ENTERPRISE LINUX 4 - DEVELOPER TOOLS GUIDE: Installation guide Installation guide Tuning guide Installation guide Manual

Contents

Chapter 1. Red Hat Cluster Suite Overview14apparent interruption to cluster clients. Cluster-service failover can occur if a cluster node fails or if acluster system administrator moves the service from one cluster node to another (for example, for aplanned outage of a cluster node).To create a high-availability service, you must configure it in the cluster configuration file. A clusterservice comprises cluster resources. Cluster resources are building blocks that you create andmanage in the cluster configuration file — for example, an IP address, an application initializationscript, or a Red Hat GFS shared partition.You can associate a cluster service with a failover domain. A failover domain is a subset of clusternodes that are eligible to run a particular cluster service (refer to Figure 1.10, “Failover Domains”).NoteFailover 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 specifyfailover priority in a failover domain. Specifying failover priority consists of assigning a priority level toeach node in a failover domain. The priority level determines the failover order — determining whichnode that a cluster service should fail over to. If you do not specify failover priority, a cluster servicecan fail over to any node in its failover domain. Also, you can specify if a cluster service is restrictedto run only on nodes of its associated failover domain. (When associated with an unrestricted failoverdomain, a cluster service can start on any cluster node in the event no member of the failover domainis available.)In Figure 1.10, “Failover Domains”, Failover Domain 1 is configured to restrict failover within thatdomain; therefore, Cluster Service X can only fail over between Node A and Node B. Failover Domain2 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 aspriority 3. If Node C fails, Cluster Service Y fails over to Node B next. If it cannot fail over to Node B, ittries failing over to Node D. Failover Domain 3 is configured with no priority and no restrictions. If thenode that Cluster Service Z is running on fails, Cluster Service Z tries failing over to one of the nodesin Failover Domain 3. However, if none of those nodes is available, Cluster Service Z can fail over toany node in the cluster.