Dependency Stuff

[Allen S. Firstenberg]

On Wed, Mar 26, 2003 at 10:47:16AM +0100, Johannes Dagemark wrote:

> Why not use the parents directive to handle host-dependency as well. I see
> no point in having the redundant configuration that we have today with
> both parents and host/service dependencies.

I think there is some confusion about the purpose of "parents" vs the
purpose of "dependencies".  Both appear to do the same thing, but are
intended for slightly different things, from what I read.

Parents are intended to map the basic network topology.  This helps Nagios
(and therefore you) determine network problems if it loses touch with
hosts.  Hosts are intended to have parents, and it is a simple configuration
option that most users will use.  If your parent goes down, you enter an
unreachable state distinct from up or down, and you can notify (or not)
based on this state.  This is simple, yet powerful, and fits most needs.  It
even works if you have multiple parents, and only sends out the unreachable
notice if it really is unreachable.  See the documentation for extensive
examples.

Dependencies are not as simple, and (to quote the manual) "are optional and
are mainly targeted at advanced users who have complicated monitoring
setups".  They're not intended to show network relationships, but to show
more complicated relationships - for a contrived example, Host A is
powered by a generator B, which is also monitored via Nagios.  There is no
Internet network between the two, so B is not a parent of A, but if B is
down, A will shut down as well, but the cause is because of B, not because
of A.  We may wish to setup a dependency relationship in this case, but not
a parent relationship.

Allen


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