[Pacemaker] Trouble with ordering

Gerald Vogt vogt at spamcop.net
Fri Sep 30 04:06:51 EDT 2011


I am running a cluster with 3 nodes. These nodes provide dns service.
The purpose of the cluster is to have our two dns service ip addresses
online at all times. I use IPaddr2 and that part works.

Now I try to extend our setup to check the dns service itself. So far,
if a dns server on any node stops or hangs the cluster won't notice.
Thus, I wrote a custom ocf script to check whether the dns service on
a node is operational (i.e. if the dns server is listening on the ip
address and whether it responds to a dns request).

All cluster nodes are slave dns servers, therefore the dns server
process is running at all times to get zone transfers from the dns

Obviously, the dns service resource must be colocated with the IP
address resource. However, as the dns server is running at all times,
the dns service resource must be started or stopped after the ip
address. This leads me to something like this:

primitive ns1-ip ocf:heartbeat:IPaddr2 ...
primitive ns1-dns ocf:custom:dns op monitor interval="30s"

colocation dns-ip1 inf: ns1-dns ns1-ip
order ns1-ip-dns inf: ns1-ip ns1-dns symmetrical=false

Problem 1: it seems as if the order constraint does not wait for an
operation on the first resource to finish before it starts the
operation on the second. When I migrate an IP address to another node
the stop operation on ns1-dns will fail because the ip address is
still active on the network interface. I have worked around this by
checking for the IP address on the interface in the stop part of my
dns script and sleeping 5 seconds if it is still there before checking
again and continuing.

Shouldn't the stop on ns1-ip first finish before the node initiates
the stop on ns1-dns?

Problem 2: if the dns service fails, e.g. hangs, the monitor operation
fails. Thus, the cluster wants to migrate the ip address and service
to another node. However, it first initiates a stop on ns1-dns and
then on ns1-ip.

What I need is ns1-ip to stop before ns1-dns. But this seems
impossible to configure. The order constraint only says what operation
is executed on ns1-dns depending on the status of ns1-ip. It says what
happens after something. It cannot say what happens before something.
Is that correct? Or am I missing a configuration option?



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