High Availability command line interface - future plans.

[Tim Penhey]

On 07/11/13 09:11, David Cheney wrote:
> +1 (million), this solution keeps coming up, and I still feel it is
> the right one.
> 
> On Thu, Nov 7, 2013 at 7:07 AM, Kapil Thangavelu
> <kapil.thangavelu at canonical.com> wrote:
>>
>> instead of adding more complexity and concepts, it would be ideal if we
>> could reuse the primitives we already have. ie juju environments have three
>> user exposed services, that users can add-unit / remove-unit etc.  they have
>> a juju prefix and therefore are omitted by default from status listing.
>> That's a much simpler story to document. how do i scale my state server..
>> juju add-unit juju-db... my provisioner juju add-unit juju-provisioner.
>>
>> -k

NOTE: removed juju at lists.ubuntu.com from the recipients;
  PLEASE DON'T CROSS-POST
Seriously!


For future direction I agree with this.  We talked about the idea behind
having the core parts of juju exposed as special services with units.
We talked about using namespaces.

I recall that Gustavo's point at the time is that we don't *need* this
to get HA, and that we can get HA much simpler to start with.

I fully support an approach where we have a simple command to get us
over the initial hump of managing support.

  juju ensure-ha  (note: not ensure-ha-state)

This brings up multiple manager nodes.

I like the idea that we treat manager nodes as special, and that
destroy-machine on them doesn't work the same way.

Consider this:

  juju boostrap
  juju ensure-ha

later machine-2 (a manager node goes down)

  juju ensure-ha

removes machine-2, and brings up machine-x to take it's place.  I was
talking with William, and I think we both agreed that we don't want to
restart manager nodes by magic, but wait for user intervention.

Now, looking to the future:

We would have services like:
  juju:db
  juju:api
  juju:something-else (for the other manager worker tasks)

bootstrap would then give machine-0 with a unit of each of these.

ensure-ha would bring up new machines with units of each of these.

A user could add two more api servers by going:

  juju add-unit juju:api -n 2

I think this gives us a clean, and understandable way of doing things,
but we SHOULD NOT do this first.

Tim