[Pacemaker] location constraint "anywhere" on asymmetric cluster

[Brian J. Murrell]

I'm experimenting with asymmetric clusters and resource location
constraints.

My cluster has some resources which have to be restricted to certain
nodes and other resources which can run on any node.  Given that, an
"opt-in" cluster seems the most manageable.  That is, it seems easier to
create constraints based on where things should run (i.e. a whitelist)
rather than having to maintain lists of where things shouldn't run
(blacklists).

I wonder though for the case of a resource that can run anywhere, if
there is any more elegant way to specify that in an asymmetric cluster
other than creating an expression using something like the "#uname"
attribute with an operation of "ne" and specifying a host that doesn't
exist for the expression's "value".

Of course other attributes could be used in a negative fashion such as
this but I wonder if there is a more "positive" syntax to express
"anywhere".  Ideally, I'd like the expression to be absolutely clear
that it's intention is to allow the resource to run "anywhere" rather
than the reader having to deduce that by knowing that the node specified
doesn't exist.

Alternatively, if there is a way to "whitelist" (i.e. meaning not having
to create and maintain a list of where not to run a resource) where
resources can run on a symmetric cluster that might be an acceptable
alternative.

Cheers,
b.

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