[ClusterLabs] Antw: Re: Antw: [EXT] Re: Sub‑clusters / super‑clusters?

[Ulrich Windl]

>>> Antony Stone <Antony.Stone at ha.open.source.it> schrieb am 04.08.2021 um
23:01 in
Nachricht <202108042301.19895.Antony.Stone at ha.open.source.it>:
> On Wednesday 04 August 2021 at 22:06:39, Frank D. Engel, Jr. wrote:
> 
>> There is no safe way to do what you are trying to do.
>> 
>> If the resource is on cluster A and contact is lost between clusters A
>> and B due to a network failure, how does cluster B know if the resource
>> is still running on cluster A or not?
>>
>> It has no way of knowing if cluster A is even up and running.
>> 
>> In that situation it cannot safely start the resource.
> 
> I am perfectly happy to have an additional machine at a third location in 
> order to avoid this split‑brain between two clusters.
> 
> However, what I cannot have is for the resources which should be running on

> cluster A to get started on cluster B.
> 
> If cluster A is down, then its resources should simply not run ‑ as happens

> right now with two independent clusters.
> 
> Suppose for a moment I had three clusters at three locations: A, B and C.
> 
> Is there a method by which I can have:
> 
> 1. Cluster A resources running on cluster A if cluster A is functional and 
> not 
> running anywhere if cluster A is non‑functional.

If cluster A is non-functional, no resoiurces of cluster A will run.

> 
> 2. Cluster B resources running on cluster B if cluster B is functional and 
> not 
> running anywhere if cluster B is non‑functional.

Likewise for cluster B.

> 
> 3. Cluster C resources running on cluster C if cluster C is functional and 
> not 
> running anywhere if cluster C is non‑functional.

Same here.

> 
> 4. Resource D running _somewhere_ on clusters A, B or C, but only a single 
> instance of D at a single location at any time.

Part of the problem is your description: Actually you do not have a resource
D, but you have three resources like D_A, D_B, and D_C

Maybe things were easier if it it would all be one big cluster with location
constraints.


> 
> Requirements 1, 2 and 3 are easy to achieve ‑ don't connect the clusters.
> 
> Requirement 4 is the one I'm stuck with how to implement.
> 
> If the three nodes comprising cluster A can manage resources such that they

> run on only one of the three nodes at any time, surely there must be a way 
> of 
> doing the same thing with a resource running on one of three clusters?
> 
> 
> Antony.
> 
> ‑‑ 
> I don't know, maybe if we all waited then cosmic rays would write all our 
> software for us. Of course it might take a while.
> 
>  ‑ Ron Minnich, Los Alamos National Laboratory
> 
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