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

[Andrei Borzenkov]

On 05.08.2021 00:01, Antony Stone wrote:
> 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.
> 
> 2. Cluster B resources running on cluster B if cluster B is functional and not 
> running anywhere if cluster B is non-functional.
> 
> 3. Cluster C resources running on cluster C if cluster C is functional and not 
> running anywhere if cluster C is non-functional.
> 
> 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.
> 
> 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.
> 

You either have single cluster and define appropriate location
constraints or you have multiple clusters and configure geo-cluster on
top of them. But you already have been told it multiple times.

> 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?
> 
> 

You need something that coordinates resources between three clusters and
that is booth.