[ClusterLabs] node1 and node2 communication time question

[Ken Gaillot]

On Wed, 2022-08-10 at 10:35 +0900, 권오성 wrote:
> Thank you for your reply.
> Then, could you explain how to activate and set the stonith?

Hi,

In normal circumstances, the cluster can tell each node what to do, and
receive confirmation. This allows the cluster to coordinate so that
resources don't run in conflict with each other.

For example, mounting an e2fs filesystem on two nodes would cause data
corruption. Bringing an IP address up on two nodes would render it
unusable because packets would randomly go to one or the other.

If cluster communication is disrupted, for example by a network card
failure or extremely high load on a node, then the cluster can't safely
start its resources elsewhere. In that situation, the node itself can't
be relied on to stop resources. The cluster must have some way of
forcing the node to be shut down or cut off from the rest of the
cluster, and that's what fencing is.

The classic example of fencing is an intelligent power switch. When a
node becomes unreachable, the rest of the cluster can tell the power
switch to cut power to the node. Then the cluster can assume the node
is not running any resources, and recover them on other nodes.

How fencing is configured depends on what you're using as nodes
(virtual machines, physical machines, cloud instances, etc.) and what
hardware you have available (IPMI, intelligent power switches, shared
storage, etc.).

> Or let me know the blog or site you know.
> I looked up the site I found and proceeded with the setting, and
> almost all the sites explained it with the setting I set.

Unfortunately, many sites do that because it's easier than trying to
explain all the ways fencing can be configured. But the result is a
cluster that's vulnerable to unrecoverable situations and data loss.

If your cluster nodes are virtual machines, and you have access to the
host, this should work:

 https://wiki.clusterlabs.org/wiki/Guest_Fencing

If you're using something else as cluster nodes, let us know.
-- 
Ken Gaillot <kgaillot at redhat.com>