[Linux-cluster] support for hierarchical services?

linux-cluster at merctech.com linux-cluster at merctech.com
Fri Sep 26 14:45:22 UTC 2008

Does RHCS5 (rgmanager-2.0.38-2.el5_2.1, cman-2.0.84-2.el5,
openais-0.80.3-15.el5) support hierarchical services, not just
resources? This doesn't seem possible via the "system-config-cluster"
tool or Luci.

For example, I've got a clustered web server. It provides several
applications, each of which has it's own resources that Apache doesn't
need to know about directly. Each application relies on Apache as a
presentation layer. I don't want to make the individual applications'
dependencies separate resources within a single "Apache" service,
because that makes management difficult.

For example, is it possible to create a structure like:

	Service:	Apache
		Private Resource:	IP address
		Private Resource:	GFS Vol1

		Shared Service:	Wiki
		Shared Service:	SVN
		Shared Service:	Calendar

	Service:	Wiki
		Private Resource:	GFS Vol2
		Private Resource:	MySQL "wiki" instance
	Service:	SVN
		Private Resource:	MySQL "svn" instance
		Private Resource:	GFS Vol3
	Service:	Calendar
			(no resources beyond apache)

Note that resources like "GFS Vol2" and "MySQL wiki instance" are assigned
to the "Wiki" service, not directly to the "Apache" service. The Apache
service sees "Wiki" as a resource.

With this kind of structure, I could administratively disable the "Wiki" service
without causing the other web applications to restart or relocate. However, if a
resource that the Wiki requires fails, the the standard failover policy would
apply...the Wiki service would restart and if that is unsuccessful, then the
Apache service (and it's dependencies--Wiki, SVN, Calendar, IP address, GFS
Vol1) would relocate.

In other words, it doesn't make sense to run the Wiki service if Apache isn't
running, but the Apache service itself doesn't depend on the MySQL "wiki"
instance resource. If the Wiki service cannot be restarted (or is
administratively disabled), the other web applications should not be affected.

Mark Bergman

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