[PVE-User] HA question

[Thomas Lamprecht]

On 10/06/2016 09:08 AM, Kevin Lemonnier wrote:
>> He wanted to remove it from HA managed but said to HA it should be
>> stopped, nothing to do with the stop/shutdown button confusion :)
> Yeah sorry about that, I hijacked this thread with my somewhat un-related
> complaint, that's my bad :).

No worries, and I hope also that I didn't discourage any from giving 
feed back.
The ha-manager did not received that much feedback, besides obvious bug 
reports.
So thanks for yours.

>
> The HA enable / disable is a bit confusing, it just doesn't work as you'd
> expect. Now that I used HA a lot more I get it, but it's a bit of a trap
> when you are starting with HA, just like the fact that only one task can
> be carried out at the same time on HA enabled VMs. I understood that only
> a few weeks ago when gluster froze a VM and that stuck HA on a task forever,
> took me a while to understand why I couldn't do anything about all of the
> other VMs.

That's the nature of the finite state machine (FSM) in the HA manager, you
can be in only one state at a time.  We think one task per time is good for
HA as multiple at the same time can have side effects, which is not good.
We want that a service is always in a defined and if possible good state.

> Or why on some VMs the live migration has an output and for others it doesn't,
> it's because for HA enabled VM you just add a task, the output is in a separate
> task.

Yes that is can be confusing I guess, it came with the architecture of the
ha-manager.
The ha-manager has quite simple mechanics internal, this makes in generally
more stable (hopefully ;)).
When it was combined it with the rest of the PVE ecosystem we tried to
integrate it without much changes there, to avoid new bugs and new code to
maintain.
that lead to things like two task per real task as the interface has not to
care if it triggers a task for a ha-managed or non-ha VM.

For the double task list I have an idea in my head, I have to try it if 
it works and
evaluate it if the changes are justified.

> Maybe it'd be good to add a visual hint about that, you aren't actually
> stoping, starting or migrating a VM, you are just adding a task for the HA to
> carry out later, and that's where you should look to see the output ? Same thing
> in HA, the enable / disable tick box could maybe be labelled "keep powered on" or
> something similar ?
>
>

The hint in the ha-managers task output is a good idea!:)

For the enable/disable things I'm hesitating, its good documented and from
the point of how the ha-manager works it makes sense, imo.
We talked internally about an "unmanaged" state in the FSM, it was just an
idea from my side and not a real need were here we decided against doing
it to let things be as simple as possible.

cheers,
Thomas