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Excerpts from Dan Prince's message of 2014-02-15 06:05:30 -0800:
> 
> ----- Original Message -----
> > From: "Robert Collins" <robertc at robertcollins.net>
> > To: "OpenStack Development Mailing List (not for usage questions)" <openstack-dev at lists.openstack.org>
> > Cc: openstack-operators at lists.openstack.org
> > Sent: Friday, February 14, 2014 11:12:12 PM
> > Subject: Re: [Openstack-operators] [openstack-dev] [TripleO] consistency vs    packages in TripleO
> > 
> > Currently we have two options for upgrading images. A) /mnt/state, B)
> > a SAN + cinder. We haven't tested B), and I expect for many installs B
> > won't be an option. /mnt/state is 100% technical, as no other options
> > exist - none of the Linux distro 'read only root' answers today answer
> > the problem /mnt/state solves in a way compatible with Nova.
> 
> I would argue that we haven't tried all of the read only root mechanism
> either... at least to the point where we can definitely don't work. Sure
> the data has to go somewhere... but it is how we present this to the
> end user that is the point in this thread, no?
> 
> All I'm arguing for here is the ability to avoid doing this to our nova.conf file (what we do today in TripleO):
> 
>  state_path=/mnt/state/var/lib/nova
> 
> And instead simply use the Nova default (/var/lib/nova) and have some
> other mechanism take care of the mapping for us (bind mounts, etc). In
> the context of end user documentation I certainly think this has less
> of an impact and is more pleasing to all.
> 

Could I divert you a bit into explaining what other readonly root schemes
exist? I've not looked into them very much as none seemed "simple" to
me when you consider that things like /var/lib/dpkg are intended to be
readonly parts of the image.

I'll start by saying that I'm very suspicious of any mechanism which tries
to intermix writable data with readonly data. A TripleO user needs only
learn once that "/mnt is preserved, everything else is not". It is also
extremely discoverable. So I am quite curious to hear what alternative
we could use that would make this simpler.