Control which nodes restart dockerd on MCR/Engine Upgrades via Launchpad

[abrainerd]

Hello,

A useful enhancement for launchpad would be to add functionality so that during an MCR/Engine upgrade, users could have the ability to specify on which nodes a restart of dockerd would occur. Some uses cases of large clusters have their upgrades performed in batches of workers, so that pods can be shifted around to avoid impact. The idea is a user could specify the specific host(s) for restarts of dockerd to occur instead of it restarting dockerd on all hosts one by one in a linear fashion. This results in less/unnecessary impact and disruption during an upgrade.

As a suggestion, perhaps a "don’t restart” flag to launchpad, which would tell launchpad to not do anything during the “Restart MCR” phase. Thank you!

Cc: @james-nesbitt