[ClusterLabs] Two-Node OCFS2 cluster keep rebooting each other

Jonathan Vargas jonathan.vargas at alkaid.cr
Thu Jun 11 15:49:32 UTC 2015


Finally we added a third node and fencing works great this way when one of
them fails. I had to use no-quorum-policy set to freeze for this
configuration  on SLES 11 SP3.
On Jun 10, 2015 9:21 AM, "Digimer" <lists at alteeve.ca> wrote:

> On 10/06/15 04:11 AM, Jonathan Vargas wrote:
> > Thanks Digimer,
> >
> > I read an old post where you mention the configuration. However after
> > adding "start-delay=15" to my stonith resource, yet both nodes reboot at
> > the same time on network disconnect.
>
> Not 'start-delay', just 'delay'.
>
> > This is my current configuration after the "start-delay" change:
> >
> > http://i.imgur.com/1o5bGvj.png
> >
> > And this is the status of the cluster:
> >
> > http://i.imgur.com/TJNsHVD.png
> >
> > I don't have a hardware stonith device, so I think linux watchdog is
> > being used.  Is ok that the stonith resource be placed on a single node?
>
> I've not used it.
>
> The test though is to see if the fencing workings when you crash each
> machine (echo c > /proc/sysrq-trigger) and when the machine is alive,
> but the network is failed.
>
> > Any idea about what should I fix?
> >
> > Thanks in advance.
> >
> >
> >
> > 2015-06-10 0:27 GMT-06:00 Digimer <lists at alteeve.ca
> > <mailto:lists at alteeve.ca>>:
> >
> >     On 10/06/15 01:50 AM, Jonathan Vargas wrote:
> >     >
> >     > 2015-06-09 23:26 GMT-06:00 Digimer <lists at alteeve.ca <mailto:
> lists at alteeve.ca>
> >     > <mailto:lists at alteeve.ca <mailto:lists at alteeve.ca>>>:
> >     >
> >     >     On 10/06/15 01:19 AM, Jonathan Vargas wrote:
> >     >     > Thanks Andrei, Digimer.
> >     >     >
> >     >     > I see. Since I need to address this discussion to a
> >     definitive solution,
> >     >     > I am sharing you a diagram of how we are designing this HA
> >     architecture,
> >     >     > to clarify the problem we are trying to solve:
> >     >     >
> >     >     > http://i.imgur.com/BFPcZSx.png
> >     >
> >     >     Last block is DRBD. If DRBD will be managed by the cluster, it
> >     must have
> >     >     fencing.
> >     >
> >     >     This is your definitive answer.
> >     >
> >     >     Without it, you *will* get a split-brain. That leads to, at
> >     best, data
> >     >     divergence or data loss.
> >     >
> >     >     > The first layer, Load Balancer; and the third later,
> >     Database, are both
> >     >     > already setup. The Load Balancer cluster uses only an VIP
> >     resource,
> >     >     > while Database cluster uses DRBD+VIP resources. They are on
> >     production
> >     >     > and work fine, test passed :-)
> >     >     >
> >     >     > Now we are handling the Web Server layer, which I am
> >     discussing with
> >     >     > experts like you. These servers require to be all active and
> >     see the
> >     >     > same data for read & write, as quickly as possible, mainly
> >     reads.
> >     >     >
> >     >     > *So, If we stay with OCFS2: *Since we need to protect the
> >     service
> >     >     > availability and keep most of nodes up, what choices do I
> >     have to avoid
> >     >     > reboots on both Web nodes caused by a split-brain situation
> >     when one of
> >     >     > them is disconnected from network?
> >     >
> >     >     None of this matters relative to the importance of working,
> tested
> >     >     fencing for replicated storage.
> >     >
> >     >     In any HA setup, the reboot of a node should matter not. If
> >     you are
> >     >     afraid of rebooting a node, you need to reconsider your design.
> >     >
> >     >
> >     >
> >     > Well, the problem is caused by a pretty common scenario: A simple
> >     > network disconnection on node 1 causes both nodes to reboot, even
> when
> >     > the node 1 is still offline, it will keep rebooting the active
> node 2.
> >     > There were no disk issues, but the service availability was lost.
> >     > *That's the main complain now :-/*
> >
> >     This is a symptom of a configuration issue. It is a separate topic
> for
> >     using/not using fencing.
> >
> >     First, don't start the cluster when the node boots.
> >
> >     A node will boot for one of two reasons only;
> >
> >     1. Node was fenced; You don't want it back into the cluster until you
> >     know it is safe to do so.
> >
> >     2. Scheduled maintenance; A human is there, so rejoining it after the
> >     maintenance is over is a non-issue.
> >
> >     This solves the fence-on-boot issue. Also, corosync's wait_for_all
> >     should be used to further protect against this.
> >
> >     If the problem is that both fence before they die, then set a delay
> >     against a node to give it a head-start in fencing the peer. I find
> >     delay="15" to be a good value.
> >
> >
> >
> > Okay. It will solve the problem about one node fencing the other one
> > after reboots. But it will require manual intervention to make the
> > service available again.
> >
> > What if I disable fencing at all, and I keep syncing a local copy of the
> > data on each node's own disk.
> >
> >
> >
> >
> >     >     > Correct me if I'm wrong:
> >     >     >
> >     >     > *1. Redundant Channel:* This is pretty difficult, since we
> would
> >     >     have to
> >     >     > add two new physical netword cards to the virtual machine
> hosts, and
> >     >     > that changes network configuration a lot in the
> virtualization platform.
> >     >
> >     >     High Availability must put priorities like hassle and cost
> second to
> >     >     what makes a system more resilient. If you choose not to spend
> the extra
> >     >     money or time, then you must accept the risks.
> >     >
> >     >
> >     >     > *2. Three Node Cluster:* This is possible, but it will
> consume more
> >     >     > resources. We can have it only for cluster communication
> though, not for
> >     >     > web processing, that will decrease load.
> >     >
> >     >     Quorum is NOT a substitution for fencing. They solve different
> problems.
> >     >
> >     >     Quorum is a tool for when all nodes are behaving properly.
> Fencing is a
> >     >     tool for when a node is not behaving properly.
> >     >
> >     >
> >     >
> >     > Yes, but by adding a 3rd node, it will help to determine which node
> >     > could be failing and which are not, to fence the proper one. Right?
> >
> >     If you have a 3rd node and you fail the network on one, then in
> theory,
> >     yes it will help. In practice, if you down the network on one node,
> it
> >     won't be able to fence the other node anyway and will be the fence
> >     victim.
> >
> >     >     > *3. Disable Fencing:* You said this should not happen at all
> if we
> >     >     use a
> >     >     > shared disk like OCFS. So I am discarding it.
> >     >
> >     >     Correct.
> >     >
> >     >     > *4. Use NFS: *Yes, this will cause a SPoF, and to solve it we
> >     >     would have
> >     >     > to setup another cluster with DRBD as described here
> >     >     >
> >     >     <
> https://www.suse.com/documentation/sle_ha/singlehtml/book_sleha_techguides/book_sleha_techguides.html
> >,
> >     >     > and add more infrastructure resources, or do we can setup
> NFS over OCFS2?
> >     >
> >     >     ... Which would require fencing anyway, so you gain nothing
> but another
> >     >     layer of things to break. First rule of HA; Keep it simple.
> >     >
> >     >     Complexity is the enemy of availability.
> >     >
> >     >
> >     >
> >     > Sure, fencing must be added to if this would be the case.
> >
> >     Fencing is always needed in HA clusters, full stop.
> >
> >
> >     --
> >     Digimer
> >     Papers and Projects: https://alteeve.ca/w/
> >     What if the cure for cancer is trapped in the mind of a person
> without
> >     access to education?
> >
> >     _______________________________________________
> >     Users mailing list: Users at clusterlabs.org <mailto:
> Users at clusterlabs.org>
> >     http://clusterlabs.org/mailman/listinfo/users
> >
> >     Project Home: http://www.clusterlabs.org
> >     Getting started:
> http://www.clusterlabs.org/doc/Cluster_from_Scratch.pdf
> >     Bugs: http://bugs.clusterlabs.org
> >
> >
> >
> >
> > _______________________________________________
> > Users mailing list: Users at clusterlabs.org
> > http://clusterlabs.org/mailman/listinfo/users
> >
> > Project Home: http://www.clusterlabs.org
> > Getting started: http://www.clusterlabs.org/doc/Cluster_from_Scratch.pdf
> > Bugs: http://bugs.clusterlabs.org
> >
>
>
> --
> Digimer
> Papers and Projects: https://alteeve.ca/w/
> What if the cure for cancer is trapped in the mind of a person without
> access to education?
>
> _______________________________________________
> Users mailing list: Users at clusterlabs.org
> http://clusterlabs.org/mailman/listinfo/users
>
> Project Home: http://www.clusterlabs.org
> Getting started: http://www.clusterlabs.org/doc/Cluster_from_Scratch.pdf
> Bugs: http://bugs.clusterlabs.org
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.clusterlabs.org/pipermail/users/attachments/20150611/6192151c/attachment.htm>


More information about the Users mailing list