Storage support?

[Clint Byrum]

Excerpts from Gustavo Niemeyer's message of Wed Jul 13 13:10:54 -0700 2011:
> > I agree that it would be very useful.  I don't know about handling it from
> > within a formula, though.  If formulas are concerned with deploying and
> > exposing services, it may not be a good idea to begin considering things
> > like block devices a service (elastic or otherwise).  I'd personally prefer
> > to see storage provisioning handled internally by ensemble in the same way
> > machines are currently launched.  This would allow ensemble to abstract away
> > the details of each storage type into the corresponding
> > provisioner/environments (EBS for EC2, SAN for Cobbler, nova-volume for
> > Openstack, etc). As an added benefit, it would keep the corresponding cloud
> > credentials in the ensemble environment and not require them to be
> > dispatched to nodes/zookeeper via formulas.
> 
> +1!  It also makes sense to me to have it internally handled.
> 
> We debated about the concept a few times, and there are quite a few
> nice things we can do by understanding the storage semantics used by a
> formula (e.g. backups, migrations, etc).
> 
> For now, though, we opted to simply use EBS at all times to avoid
> handling yet another problem right now, and to ensure people their
> data won't magically disappear if the machine is shut down for
> whatever reason.

I agree as well that this is something ensemble needs to be capable of doing.

Basically at some point it will be useful to be able to say something like

ensemble deploy mysql super-awesome-db data:size=100G

And have the formula define that it has "data", and that it should be
mounted in such a way (/var/lib/mysql for instance), and have a hook
'volume-data-snapshot' which can run a flush command or a freeze command
or whatever is needed to make sure the snapshot is consistent.

Then you can say:

ensemble snapshot-service super-awesome-db:data
INFO: snapshot created, super-awesome-db:data/0

Which would really be multiple snapshots, one for each service unit.

Do it again

ensemble snapshot-service super-awesome-db:data
INFO: snapshot created, super-awesome-db:data/1

Then it gets interesting, because you can do

ensemble deploy mysql super-awesome-testing-db --using-snapshot super-awesome-db:data/0

And the holy grail..

ensemble migrate super-awesome-db super-awesomer-db --instance-type=x99.mega-chunka-honking-large

Which would make new machines, freeze the old ones, start the new ones,
and then move all the relations to the new ones.

Right.. ok, Ensemble 2017 plans are set. ;)