[Info-vax] Quorum strategy

[Stephen Hoffman]

On 2019-05-22 08:44:59 +0000, Marc Van Dyck said:

> First question : did I get that right ?

Clustering does have a concept of a primary for the connection manager, 
but does not otherwise present that to the app-level processing.

In the absence of the possibility to update the code, and in the 
absence of the possibility of writing some code to automatically 
perform the app transition from secondary to primary, or to—for 
instance—scan for the lowest-addressed host when more than one host is 
present in the cluster...

The whole reason the quorum disk was implemented was to avoid the need 
for a primary-secondary configuration.  And that primary-secondary 
configuration is what you want here.

Give one vote to the cluster member host that you're referring to as 
the primary.  Remove the quorum disk. Give no votes for the secondary.

The secondary is operating as only a little more than a warm standby, 
here.  Yes, it can be configured to run some apps.

Since you reboot to promote the secondary to primary, that reboot can 
be with an added vote, and this only when the primary can be left 
hard-down.

Could well be one boot root to boot as secondary, and another boot root 
to boot as primary.  Or write a manual process that tweaks the relevant 
system parameters.

Downside: if the failed primary reboots and rejoins the party, you'll 
have two hosts that both want to be "primary".  Much like adding code 
for the transition, it's also possible to code some checks at startup 
to detect and block a second host from becoming primary.



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