On 18/09/14 09:29, Andrew Beekhof wrote:
On 18 Sep 2014, at 6:18 pm, Christine Caulfield <ccaulfie@xxxxxxxxxx> wrote:
On 18/09/14 02:35, Andrew Beekhof wrote:
On 18 Sep 2014, at 12:34 am, Vallevand, Mark K <Mark.Vallevand@xxxxxxxxxx> wrote:
Thanks.
1. I didn't know about two-node mode. Thanks. We are testing with two nodes and "crm configure property no-quorum-policy=ignore". When one node goes down, the other node continues clustering. This is the desired behavior. What will <cman two_node="1" expected_votes="1"> </cman> in cluster.conf do?
I was all set to be a smart-ass and say 'man cluster.conf', but the joke is on me as my colleagues do not appear to have documented it anywhere.
Chrissie: Can you elaborate on the details here please?
it's documented in the cman(5) man page. The entries in cluster.conf only cover the general parts that are not specific to any subsystem. So corosync items are documented in the corosync man page and cman ones in the cman man page etc.
Ah! Good to know.
Two node clusters
Ordinarily, the loss of quorum after one out of two nodes fails will prevent the remaining node from continuing (if both nodes have one vote.) Special configuration options can be set to allow the one remaining node to continue operating if the other
fails. To do this only two nodes, each with one vote, can be defined in cluster.conf. The two_node and expected_votes values must then be set to 1 in the cman section as follows.
<cman two_node="1" expected_votes="1">
</cman>
One thing thats not clear to me is what happens when a single node comes up and can only see itself.
Does it get quorum or is it like wait-for-all in corosync2?
There's no wait_for_all in cman. The first node up will attempt (after
fence_join_delay) the other node in an attempt to stop a split brain.
This is one of several reasons why we insist that the fencing is on a
separate network to heartbeat on a two_node cluster.
Chrissie
Chrissie
(Short version, it should do what you want)
2. Yes, fencing is part of our plan, but not at this time. In the configurations we are testing, fencing is a RFPITA.
3. We could move up. We like Ubuntu 12.04 LTS because it is Long Term Support. But, we've upgraded packages as necessary. So, if we move to the latest stable Pacemaker, Cman and Corosync (and others?), how could this help?
Well you might get 3+ years of bug fixes and performance improvements :-)
Is there a way to get the clustering software to 'poll' faster? I mean, this NIC stalling at boot time only lasts about 2 seconds beyond the start of corosync. But, its 30 more seconds before the nodes see each other. I see lots of parameters in the totem directive that seem interesting. Would any of them be appropriate.
Is there not a way to tell upstart not to start the cluster until the network is up?
Andrew: Thanks for the prompt response.
Regards.
Mark K Vallevand
"If there are no dogs in Heaven, then when I die I want to go where they went."
-Will Rogers
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-----Original Message-----
From: linux-cluster-bounces@xxxxxxxxxx [mailto:linux-cluster-bounces@xxxxxxxxxx] On Behalf Of Andrew Beekhof
Sent: Tuesday, September 16, 2014 08:51 PM
To: linux clustering
Subject: Re: Cman (and corosync) starting before network interface is ready
On 17 Sep 2014, at 7:20 am, Vallevand, Mark K <Mark.Vallevand@xxxxxxxxxx> wrote:
It looks like there is some odd delay in getting a network interface up and ready. So, when cman starts corosync, it can't get to the cluster. So, for a time, the node is a member of a cluster-of-one. The cluster-of-one begins starting resources.
1. enable two-node mode in cluster.conf (man page should indicate where/how) then disable no-quorum-policy=ignore
2. configure fencing
3. find a newer version of pacemaker, we're up to .12 now
A few seconds later, when the interface finally is up and ready, it takes about 30 more seconds for the cluster-of-one to finally rejoin the larger cluster. The doubly-started resources are sorted out and all ends up OK.
Now, this is not a good thing to have these particular resources running twice. I'd really like the clustering software to behave better. But, I'm not sure what 'behave better' would be.
Is it possible to introduce a delay into cman or corosync startup? Is that even wise?
Is there a parameter to get the clustering software to poll more often when it can't rejoin the cluster?
Any suggestions would be welcome.
Running Ubuntu 12.04 LTS. Pacemaker 1.1.6. Cman 3.1.7. Corosync 1.4.2.
Regards.
Mark K Vallevand
"If there are no dogs in Heaven, then when I die I want to go where they went."
-Will Rogers
THIS COMMUNICATION MAY CONTAIN CONFIDENTIAL AND/OR OTHERWISE PROPRIETARY MATERIAL and is thus for use only by the intended recipient. If you received this in error, please contact the sender and delete the e-mail and its attachments from all computers.
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