Deploying multiple applications to a single environment?

[Clint Byrum]

Excerpts from Marcos Barbosa's message of 2012-11-13 10:12:20 -0800:
> 2012/11/13 Sam Juvonen <sam.juvonen at canonical.com>
> 
> >  On 11/12/2012 02:33 PM, Marco Ceppi wrote:
> >
> > usage: deploy-to [-h] [--environment ENVIRONMENT] [--repository REPOSITORY]
> >                  [--config CONFIG]
> >                  machine charm [service_name]
> >
> > I don't recommend using this in production, as there are known problems
> > with this method. One such issues is caused when deploying things to the
> > same machine to rapidly in succession, which will cause locking issues with
> > dpkg.
> >
> >
> > What other problems does this create? If you have pointers to discussions
> > about them, that would be awesome.
> >
> Sam,
> 
> The problem is:
> 
> There's no queue for deploys. If you deploy app 2 too fast after app 1, may
> be dpkg still running and app 2 deploy crash. There's no queue for this and
> I think may be exceptions treatment not be the best.
> 

In theory most of these errors will be detected and you can just use

juju resolved unit/# --retry

And things will progress.

But, suffice to say this ruins the automation.

We're looking at providing an interface to aptdaemon, but one problem
with that is that aptdaemon itself is not included on servers, so that
apt-get would also need to be serialized.

Another problem is just that charms are written in isolation, so its
possible they will step on each others' toes.