[Pacemaker] Understanding virtual IP migration

Ken Gaillot kjgaillo at gleim.com
Mon Aug 4 18:01:15 EDT 2014

On 07/30/2014 03:15 AM, Arjun Pandey wrote:
> Apologies for the delayed response. Well i am using IPAddr2 resource.
> I don't configure the addresses statically. It gets configured when
> pacemaker starts this resource.Failure handling of this link(when i
> manually bring the link down ) also works. It's just that even though
> the IP has moved.
> If you bring the failed link back again it still has that IP address.I
> have a 2 node(Active-Standby) cluster with 2 virtual IP's
> configured.Hence stonith is also disabled.

There's not enough information here to guess what's wrong. I suggest 
going line-by-line through your "crm configure show" and comparing 
against the documentation and examples to make sure you understand how 
to make a resource run on one node or multiple nodes. Also, it's 
possible that when you brought the link back up, pacemaker moved the IP 
back to it.

If you don't have any stonith, and you disconnect the only network 
connection between the nodes, then the expected behavior is a 
split-brain situation, where both nodes bring up the IPs. The purpose of 
stonith is to prevent such a situation by having one of the nodes shut 
down the other if communication fails. If you're sure you don't want to 
use stonith, then you need to maintain network communication between 
your nodes as reliably as possible.

> On Thu, Jul 24, 2014 at 12:00 AM, Ken Gaillot <kjgaillo at gleim.com> wrote:
>> On 07/23/2014 12:15 AM, Arjun Pandey wrote:
>>> I am using virtual IP resource on  a 2 node (Active-Passive) cluster.
>>> I was testing the migration of IP address. Moving the link down moves
>>> the IP over to the other node. However if i bring interface up on the
>>> node the VIP is still associated with this interface. Shouldn't we
>>> have removed this when we decided to migrate the IP in the first place
>>> ?
>>> Also on a related note plugging out the cable, doesn't lead to IP
>>> migration. I checked the IPAddr monitor logic which simply checks if
>>> the address is still associated with the interface. However shouldn't
>>> we be checking link state as well using ethtool.
>> Hello Arjun,
>> Pacemaker can certainly do what you want, but the configuration has to be
>> exactly right. Can you post what configuration you're using?
>> Based on the information provided, one guess is that you might have the IP
>> statically configured on the interface (outside pacemaker), so that when you
>> bring the interface up, the static configuration is taking effect. When a
>> resource is managed by pacemaker, it should not be configured to start or
>> stop by any other means.
>> Regarding the pull-the-cable test, what is your networking setup? Does each
>> cluster node have a single network connection, or do you have a dedicated
>> link for clustering traffic? Do you have any sort of STONITH configured?

-- Ken Gaillot <kjgaillo at gleim.com>
Network Operations Center, Gleim Publications

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