Re: Problems to get larger user base ... (Re: [Caml-list] OCaml's variables)

[Francois Berenger <berenger@riken.jp>]

On 05/30/2013 02:05 PM, Chet Murthy wrote:
>
> I'm glad we're having this discussion.
>
> On Thursday, May 30, 2013 06:52:25 AM Malcolm Matalka wrote:
>> I think out would be wrong for opam to try to solve this problem.  There
>> are already many tools available for deploying (Ansible, Puppet, Chef,
>> Fabric, Capistrano).  Such a later can be build on top of opam of need be.
>
> I think this is incorrect.  Let me explain.
>
> (1) when we look at deploying complex collections of code/libs/data
> onto multiple machines, usually we assume that the code has already
> been built.
>
> (2) but let's first dispatch the case where the code has -not- been
> built.  In such a case, I presume you're proposing that the code be
> built on each machine, yes?
>
>    (a) this drastically increases the CPU required to perform upgrades
>    and deploys
>
>    (b) but far, far, far more importantly, it means that on each
>    machine, a nontrivially complex script runs that builds the actual
>    installed binaries.  If that script contains -any- nondeterminism or
>    environmental sensitivity, it could produce different results on
>    different machines.  The technical term is "version skew".

      (c) that's too damn slow

> In scale-out systems, this sort of "skew" is absolutely fatal, because
> it means that machines/nodes are not a priori interchangeable.  And
> all of fast-fail fault-tolerance depends on nodes being
> interchangeable.
>
> (3) But let's say that what you really mean is that we should use
> tools like puppet/chef/capistrano to copy collections of
> binaries/libs/data to target machines and install them.  These
> scripts/recipes are written by some person.  You could have equally
> well suggested that that person build Debian packages (or RPMs) of
> each OPAM package, writing out all the descriptions and manifests.
>
> And manually specifying all dependencies and requiremeents.
>
> Either way, that person is doing a job that OPAM already does a lot
> of, and does quite well.  Gosh, wouldn't it be nice if OPAM could
> generate those RPMs?  Well, it's a little more complicated than that,
> but really, not much more.  The complexity comes in that you -might-
> (I'm not saying I have this part figured out yet) want ways to
> -generalize- (say) the camlp5 package so that it could be installed on
> many different base OPAM installations.
>
> But setting aside that nice-to-have, imagine that OPAM knew how to
> generate RPMs from each package it installed, and from the ocaml+opam
> base itself.  You combine those, and you can:
>
>    (i) install ocaml, opam, and a bunch of packages
>
>    (ii) push a button, and out come a pile of RPMs, along with
>    dependencies amongst them (and hopefully on the relevant
>    environmental RPMs (e.g., libpcre-dev for pcre-ocaml, etc) so that
>    you can just stuff those RPMs into a YUM repo, go to a second box,
>    and say
>
>      "yum install opam ocaml pcre-ocaml"
>
>    and get everything slurped down and installed, just as if OPAM had
>    installed it all, package-by-package.
>
> --chet--
>
> P.S. And this doesn't even get into the unsuitability of chef/puppet
> for managing software package installation.  There's a reason that no
> distro uses such schemes to install the large and complex sets of
> packages needed to run amodern Linux box.  And why there is no Linux
> version of Microsorft's "DLL Hell".  Linux distros by and large (and
> esp Debian and Ubuntu) have worked hard to make package installation
> foolproof -- and chef/puppet etc are anything but.
>
>