[Freeipa-devel] idempotent installer [from LinuxAlt 2013]

[Derek Moore]

As someone who has fought with using/modifying/QA'ing unstable FreeIPA
installers from the nightly repos, I wholeheartedly second this motion!

Make sure the oVirt guys get wind of this idea also! ;)

PS: semi-related note — Can FreeIPA be made to consume the CSR that results
from the ovirt-host-deploy hoster node installer?

On Thursday, November 14, 2013, Petr Spacek wrote:

> Hello,
>
> there is an interesting idea that installers should be idempotent. I have
> heard it on LinuxAlt conference 2013 in Brno, Czech republic and it is
> implemented e.g. by project Chef [1] and it is used e.g. by OpenStack
> installer [2] (used e.g. by SUSE).
>
> What Wikipedia says about idempotence [3]:
> "Idempotence is the property of certain operations in mathematics and
> computer science, that can be applied multiple times without changing the
> result beyond the initial application."
>
> ... And that is it :-)
>
> In reality, it means that you can re-run OpenStack installer on the same
> machine/set of machines (with the same configuration, of course!) and it
> will re-do everything again. You can re-run installer again and again
> without any harm!
>
> This solves case where something went wrong during the installation, the
> installation was aborted and the machine was left in some inconsistent
> state. Think about e.g. network failure during installation, improper
> configuration which prevented installation from finishing (crap in DNS),
> some intermittent and mysterious errors in Dogtag installer and so on.
>
> It does mean that you don't need to recycle whole machine if something
> went wrong during installation ...
>
> As a result, you don't need to have separate system for installation and
> for upgrade.
>
> (Obviously, it means installation steps has to be 'declarative' instead of
> 'imperative'.)
>
>
> I think that this is very interesting idea and it would be interesting to
> write new code with idempotence in mind. Eventually, we could end with
> fully idempotent installer :-)
>
> [1] http://www.opscode.com/chef/
> [2] http://www.slideshare.net/mattray/deploying-openstack-with-chef
> [3] http://en.wikipedia.org/wiki/Idempotence
>
> --
> Petr^2 Spacek
>
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