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Thanks for answering. It helps.</div>
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>Main scenario where poison pill shines is 2-node-clusters where you don't<br>
>have usable quorum for watchdog-fencing.</div>
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Not sure i understand. As if just 2 node and one node fails it cannot respond to the poision pilll. Maybe i mis your point.</div>
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This also begs the followup question, what defines "usable quroum". Do you mean for example on seperate independent network hardware and power supply?</div>
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>Configured with pacemaker-awareness - default - availability of the shared-disk doesn't become an issue as, due to fallback to availability of the 2nd node, the disk is >no spof (single point of failure) in these clusters.</div>
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I did not get the jist of what you are trying to say here. 🙂<br>
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>Other nodes btw. can still kill a node with watchdog-fencing. I</div>
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How does that work when would the killing node tell the other node not to keep triggering its watchdog? </div>
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Having written the above sentence maybe it should go and read up when does the poison pill get sent by the killing node!</div>
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>If the node isn't able to accept that wish of another</div>
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>node for it to die it will have lost quorum, have stopped triggering the watchdog anyway.</div>
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Yes that is clear to mean the self-fencing is quite powerful.</div>
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Thanks for the response.</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Users <users-bounces@clusterlabs.org> on behalf of users-request@clusterlabs.org <users-request@clusterlabs.org><br>
<b>Sent:</b> 10 October 2024 2:00 PM<br>
<b>To:</b> users@clusterlabs.org <users@clusterlabs.org><br>
<b>Subject:</b> Users Digest, Vol 117, Issue 5</font>
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Today's Topics:<br>
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1. Re: Fencing Approach (Klaus Wenninger)<br>
<br>
<br>
----------------------------------------------------------------------<br>
<br>
Message: 1<br>
Date: Wed, 9 Oct 2024 19:03:09 +0200<br>
From: Klaus Wenninger <kwenning@redhat.com><br>
To: Cluster Labs - All topics related to open-source clustering<br>
welcomed <users@clusterlabs.org><br>
Cc: Angelo Ruggiero <angeloruggiero@yahoo.com><br>
Subject: Re: [ClusterLabs] Fencing Approach<br>
Message-ID:<br>
<CALrDAo332oqdTEMX82nc-BPWJ=Ea4n_citY71HLamSOv3Kw-cA@mail.gmail.com><br>
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On Wed, Oct 9, 2024 at 3:08?PM Angelo Ruggiero via Users <<br>
users@clusterlabs.org> wrote:<br>
<br>
> Hello,<br>
><br>
> My setup....<br>
><br>
><br>
> - We are setting up a pacemaker cluster to run SAP runnig on RHEL on<br>
> Vmware virtual machines.<br>
> - We will have two nodes for the application server of SAP and 2 nodes<br>
> for the Hana database. SAP/RHEL provide good support on how to setup the<br>
> cluster. ?<br>
> - SAP will need a number of floating Ips to be moved around as well<br>
> mountin/unmounted NFS file system coming from a NetApp device. SAP will<br>
> need processes switching on and off when something happens planned or<br>
> unplanned.I am not clear if the netapp devic is active and the other site<br>
> is DR but what i know is the ip addresses just get moved during a DR<br>
> incident. Just to be complete the HANA data sync is done by HANA itself<br>
> most probably async with an RPO of 15mins or so.<br>
> - We will have a quorum node also with hopefully a seperate network<br>
> not sure if it will be on a seperate vmware infra though.<br>
> - I am hoping to be allowed to use the vmware watchdog although it<br>
> might take some persuading as declared as "non standard" for us by our<br>
> infra people. I have it already in DEV to play with now.<br>
><br>
> I managed to set the above working just using a floating ip and a nfs<br>
> mount as my resources and I can see the following. The self fencing<br>
> approach works fine i.e the servers reboot when they loose network<br>
> connectivity and/or become in quorate as long as they are offering<br>
> resources.<br>
><br>
> So my questions are in relation to further fencing .... I did a lot of<br>
> reading and saw various reference...<br>
><br>
><br>
> 1. Use of sbd shared storage<br>
><br>
> The question is what does using sbd with a shated storage really give me.<br>
> I need to justify why i need this shared storage again to the infra guys<br>
> but to be honest also to myself. I have been given this infra and will<br>
> play with it next few days.<br>
><br>
><br>
> 2. Use of fence vmware<br>
><br>
> In addition there is the ability of course to fence using the fence_vmware<br>
> agents and I again I need to justify why i need this. In this particular<br>
> cases it will be a very hard sell because the dev/test and prod<br>
> environments run on the same vmware infra so to use fence_vmware would<br>
> effectively mean dev is connected to prod i.e the user id for a dev or test<br>
> box is being provided by a production environment. I do not have this<br>
> ability at all so cannot play with it.<br>
><br>
><br>
><br>
> My current thought train...i.e the typical things i think about...<br>
><br>
> Perhaps someone can help me be clear on the benefits of 1 and 2 over and<br>
> above the setup i think it doable.<br>
><br>
><br>
> 1. gives me the ability to use poison pill<br>
><br>
> But what scenarios does poison pill really help why would the other<br>
> parts of the cluster want to fence the node if the node itself has not<br>
> killed it self as it lost quorum either because quorum devcice gone or<br>
> network connectivity failed and resources needs to be switched off.<br>
><br>
> What i get is that it is very explict i.e the others nodes<br>
> tell the other server to die. So it must be a case initiated by the other<br>
> nodes.<br>
> I am struggling to think of a scenarios where the other<br>
> nodes would want to fence it.<br>
><br>
<br>
Main scenario where poison pill shines is 2-node-clusters where you don't<br>
have usable quorum for watchdog-fencing.<br>
Configured with pacemaker-awareness - default - availability of the<br>
shared-disk doesn't become an issue as, due to<br>
fallback to availability of the 2nd node, the disk is no spof (single<br>
point of failure) in these clusters.<br>
Other nodes btw. can still kill a node with watchdog-fencing. If the node<br>
isn't able to accept that wish of another<br>
node for it to die it will have lost quorum, have stopped triggering the<br>
watchdog anyway.<br>
<br>
Regards,<br>
Klaus<br>
<br>
><br>
> Possible Scenarios, did i miss any?<br>
><br>
> - Loss of network connection to the node. But that is covered by the<br>
> node self fencing<br>
> - If some monitoring said the node was not healthly or responding...<br>
> Maybe this is the case it is good for but then it must be a partial failure<br>
> where the node is still part fof the cluster and can respond. I.e not OS<br>
> freeze or only it looses connection as then the watchdog or the self<br>
> fencing will kick in.<br>
> - HW failures, cpu, memory, disk For virtual hardware does that<br>
> actually ever fail? Sorry if stupid question. I could ask our infra guys<br>
> but....,<br>
> So is virtual hardware so reliable that hw failures can be ignored.<br>
> - Loss of shared storage SAP uses a lot of shared storage via NFS. Not<br>
> sure what happens when that fails need to research it a bit but each node<br>
> will sort that out itself I am presuming.<br>
> - Human error: but no cluster will fix that and the human who makes a<br>
> change will realise it and revert. ?<br>
><br>
> 2. Fence vmware<br>
><br>
> I see this as a better poision pill as it works at the hardware<br>
> level. But if I do not need poision pill then i do not need this.<br>
><br>
> In general OS freezes or even panics if take took long are covered by the<br>
> watchdog.<br>
><br>
> regards<br>
> Angelo<br>
><br>
><br>
><br>
><br>
><br>
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