Installation guide

7.5 Dependencies
7.5.1 Resource Dependencies
The resources within a cluster service follow two different dependency rules.
First, the nesting within the service configuration defines startup order and resource
dependencies.
In the following example, resource2 depends on resource1. In addition, resource1 is started
prior to starting resource2.
<service>
<resource name=“resource1“>
<resource name=“resource2“>
</resource>
</resource>
</service>
Second, an implicit order and dependency is defined. The following lists the implicit startup
order of the previously defined resources:
1. fs
2. netfs
3. ip
4. other
7.5.2 Service Dependencies
The services in a cluster sometimes require some dependency rules; e.g., sometimes a
database must be started prior to starting the application server. However, if the database
fails and is subsequently relocated, the application server should survive. Additionally, SAP
enqueue replication requires a special type of dependency. The enqueue server must always
follow the replicated enqueue.
7.5.2.1 Hard and Soft Dependencies
The rgmanager service defines inter-service dependencies with soft and hard requirements. A
hard dependency would cause the dependent service to be stopped/started if its dependency
were stopped/started.
A soft dependency is only valid for initial startup. The dependent service would not be
stopped if its dependency were stopped.
The following example defines the service configuration for a soft dependency:
<service name=“service1“/>
<service name=“service2“ depend=“service:service1“ depend_mode=“soft“/>
Note that central_processing must be enabled to enable hard and soft service dependencies.
52 | www.redhat.com