[ClusterLabs] Two-Node OCFS2 cluster keep rebooting each other
Digimer
lists at alteeve.ca
Wed Jun 10 15:19:36 UTC 2015
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?
>
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--
Digimer
Papers and Projects: https://alteeve.ca/w/
What if the cure for cancer is trapped in the mind of a person without
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