Installation guide

Chapter 3. RGManager
RGManager manages and provides failover capabilities for collections of cluster resources called
services, resource groups, or resource trees. These resource groups are tree-structured, and have
parent-child dependency and inheritance relationships within each subtree.
How RGManager works is that it allows administrators to define, configure, and monitor cluster
services. In the event of a node failure, RGManager will relocate the clustered service to another node
with minimal service disruption. You can also restrict services to certain nodes, such as restricting
httpd to one group of nodes while mysq l can be restricted to a separate set of nodes.
There are various processes and agents that combine to make RGManager work. The following list
summarizes those areas.
Failover Domains - How the RGManager failover domain system works
Service Policies - Rgmanager's service startup and recovery policies
Resource Trees - How rgmanager's resource trees work, including start/stop orders and
inheritance
Service Operational Behaviors - How rgmanager's operations work and what states mean
Virtual Machine Behaviors - Special things to remember when running VMs in a rgmanager
cluster
ResourceActions - The agent actions RGManager uses and how to customize their behavior from
the cl uster.co nf file.
Event Scripting - If rgmanager's failover and recovery policies do not fit in your environment, you
can customize your own using this scripting subsystem.
3.1. Failover Domains
A failover domain is an ordered subset of members to which a service may be bound. Failover
domains, while useful for cluster customization, are not required for operation.
The following is a list of semantics governing the options as to how the different configuration
options affect the behavior of a failover domain.
preferred node or preferred member: The preferred node was the member designated to run a
given service if the member is online. We can emulate this behavior by specifying an unordered,
unrestricted failover domain of exactly one member.
restricted domain: Services bound to the domain may only run on cluster members which are also
members of the failover domain. If no members of the failover domain are available, the service is
placed in the stopped state. In a cluster with several members, using a restricted failover domain
can ease configuration of a cluster service (such as httpd), which requires identical configuration
on all members that run the service. Instead of setting up the entire cluster to run the cluster
service, you must set up only the members in the restricted failover domain that you associate with
the cluster service.
unrestricted domain: The default behavior, services bound to this domain may run on all cluster
members, but will run on a member of the domain whenever one is available. This means that if a
service is running outside of the domain and a member of the domain comes online, the service
will migrate to that member, unless nofailback is set.
ordered domain: The order specified in the configuration dictates the order of preference of
⁠Chapt er 3. RG Manager
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