[Linux-cluster] Service Group Dependency

[Lon Hohberger]

On Thu, 2008-11-13 at 15:28 +0100, Mauro Casiraghi wrote:
> If i have two or more services how can set dependency for the services
> using Redhat Cluster Suite??
>  
> For example if i have service A B end C how can set those dependency:
>  
> B depend from A and C depend from B
>  
> In this case to stop service group A i must stop before C and B
>  
> What is the cluster.conf setting ??

That depends.  Starting services is done in the "right" order internally
using the 'depend=' service attribute, but it's done backwards for
'stop' (e.g. stopping A will cause 'dependent' services to subsequently
stop, not stop before A).

Rgmanager has an event-action processor you can use to make this work,
(it's not a typical dependency engine, though).  You'd have to:

  (a) codify the actions necessary
  (b) enable central_processing
  (c) set up an event trigger to catch an event *before* a service
transitions and make some decisions.

A-+->B
  |
  +->C

...should be easy...

A->B->C

...would be more difficult.

There's a (very) experimental dependency engine / transition
calculator / etc. in the master branch of git which uses an A* search,
but it's not likely that we will be integrating it...

-- Lon