[ClusterLabs] Why my node1 couldn't back to the clustering chain?

[Antony Stone]

On Thursday 08 April 2021 at 16:55:47, Ken Gaillot wrote:

> On Thu, 2021-04-08 at 14:32 +0000, Jason Long wrote:
> > Why, when node1 is back, then web server still on node2? Why not
> > switched?
> 
> By default, there are no preferences as to where a resource should run.
> The cluster is free to move or leave resources as needed.
> 
> If you want a resource to prefer a particular node, you can use
> location constraints to express that. However there is rarely a need to
> do so; in most clusters, nodes are equally interchangeable.

I would add that it is generally preferable, in fact, to leave a resource 
where it is unless there's a good reason to move it.

Imagine for example that you have three nodes and a resource is running on 
node A.

Node A fails, the resource moves to node C, and node A then comes back again.

If the resource then got moved back to node A just because it had recovered, 
you've now had two transitions of the resource (each of which means *some* 
downtime, however small that may be), whereas if it remains running on node C 
until such time as there's a good reason to move it away, you've only had one 
transition to cope with.


Antony.

-- 
"The future is already here.   It's just not evenly distributed yet."

 - William Gibson

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