2.4 enable ha no presence check

Question

Description of change

This changes juju enable-ha to no longer demote/remove controller machines. This simplifies the enable-ha logic significantly, and means we don't need some of our old workarounds (like forcing the machine we are running on to not be treated as unavailable).

QA steps

$ juju bootstrap
$ juju enable-ha
$ kill/stop machine 1
$ juju enable-ha

Should no longer try to remove machine 1 from being a controller, and won't start a machine 3. Instead, doing:

$ juju remove-machine 1
$ juju enable-ha

Should give the user the ability to do exactly as they requested.

Documentation changes

This is one of the major changes of 2.4 vs previous releases. We're helping users to be explicit in how they want to change the controllers that are running, instead of hoping the side-effect of juju enable-ha would do what they want.

Bug reference

lp:1658033 lp:1703040

该提问来源于开源项目：juju/juju

Answer 1

I'm not sure what extra context I can give you for documentation. But essentially how to manage HA controllers is changing in Juju 2.4. In prior releases, "juju enable-ha" was responsible for both creating new machines to be controllers, and to demote machines that were seen as unavailable, and to remove those machines. In 2.4, we are changing the basic structure such that: 1. juju enable-ha ensures that you have N controllers (default 3). It will launch new machines if you currently have less than the desired amount. 2. The way to remove controller machines is now just juju remove-machine -m controller X. (this used to be prevented unless juju enable-ha had flagged the machine as ok to remove.) 3. The above should work if the machine is running or if it is dead. If you are in HA=3, and you remove one machine, we will change the HA structure such that only the primary has a "voting" right, but the other controller machine is kept as a hot standby (It should stay up to date with any changes being made, but will not ever be promoted to master without user intervention). To restore HA=3 simply run juju enable-ha again. 4. As before, you can chose to juju enable-ha with n=3,5,7. We don't allow you to explicitly request an even number of controllers, though you can get there via juju remove-machine. The recommendation is to always keep an odd number if you really want reliable HA.