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To: gentoo-soc@g.o
From: "Nirbheek Chauhan" <nirbheek.chauhan@...>
Subject: Progress report - AutotuA (formerly "Automate it All")
Date: Mon, 16 Jun 2008 12:28:37 +0530
It's only been a little more than a week since I started working on
the project (due to personal reasons), and my time spent to work ratio
is extremely bad, so I'm sorry but the progress isn't as much as I had
hoped.

The idea has undergone significant changes in the time passed, and
thanks to Patrick's guidance (and constant cluebats), I now have a far
more clear-cut idea of how the whole thing will come together. I
wonder whether I should describe the project blueprint that we've come
up with, the path that led to it, or what all code I have written. I
suppose the progress of the code written cannot be judged unless one
knows the whole plan, and the path taken to come up with the plan is
largely irrelevant :)

The general idea has changed somewhat from the abstract:

As before, there is a master server which acts a storage area, manages
all the slaves and does various bookkeeping. This part will be written
in Django.

The concept of the slave has changed radically to allow for a less
steep learning curve. The project described "jobs" which consist of
executables stored on the master-server which could be fetched and run
by the slaves. We thought of ways in which we could describe
dependencies between the slaves, and the most obvious answer to me was
an XML format (much to the disgust of Patrick).

However, there were numerous problems with such an approach (least of
which was the overhead involved with parsing XML and the jing deps on
the Django side for it). The most serious of these was the fact that
learning a new XML format and writing custom executables (scripts or
otherwise) which communicate with the server via the Slave's bindings
has an *extremely* steep learning curve, and will cause chaos. The
project is useless if no one ends up using it, or it gets too
complicated to use.

The solution came to me in the form of a "Doh!" moment as I was
cycling back to my room. The answer was -- "jobuilds". Bash scripts
are easily adaptable, easy to understand and use (for Gentoo devs),
and their parsing is well-understood. For the second time in my life,
I appreciated the ingenuity of the inventors of the ebuild format.


Jobuilds:
----------
A jobuild is the smallest possible "quantum" of work. A job consists
of a root jobuild which has dependencies on other jobuilds, and all
these taken together form a job. The format of a jobuild is:
http://pastebin.osuosl.org/8355

- The four phases are to be run (by default) in the chroot where the
job will take place.
- SRC_URI are programs: test suites etc which are required by the
jobuild (does not include the deps which will be pulled in by emerge
in the chroot).
- PORTCONF_URI are tarballs which will contain portage config files
(/etc/portage/* /etc/make.conf etc)
- DEPEND are other jobuilds on which this jobuild _hard_ depends, ie
they must be completed in the same chroot (example: Test Amarok
depends on Build KDE which depends on Build X)
- SIDEPEND are SuperImpose Depends, all we need to know is that those
jobuilds completed successfully *somewhere* so that further
distribution of work is possible. (example: testing if all the
packages that import gnome2.eclass still work after some changes to
it)

SRC_URI will be downloaded before entering the chroot, stored in a
tarballs folder, and hardlinked (if on the same device), or bind
mounted inside the chroot.

To counter the problem of recursive QA checking, the jobuild format
will be *extremely* simple. That means no EAPI, no eclasses, no SLOTS,
minimal versioning (xxx.yyy), no fancy depends (except perhaps ||).
Built-in functions such as unpack() etc will be provided of course.

The loss of utility from there not being eclasses will be offset
through the concept of "Template jobuilds" (similar in concept to how
Django handles Templates[1]). However, I am open to including eclasses
in the design (who doesn't love them? :) if enough reasons can be
given.

NOTE: It will be highly recommended that the autotua work folder be on
the same device. I've assumed this to be true to allow a number of
optimisations, but I will keep (slower) fallbacks in case that is not
true.


The Tree:
-----------
Obviously the jobuilds will be stored in a structured format similar
to the portage tree :^)
And following the tradition of being completely unimaginative, it
shall be called the "Jobtage tree".
The structure is as follows:

${user}/
    ${user}.asc
    ${jobuild_name}/
        ${jobuild_name}-${ver}.jobuild
        Manifest

The tree will be stored in bzr, with an overlays/ directory in .bzrignore
jobuilds will not be manifested, and will only be signed with the
maintainer's gpg key
SRC_URI and PORTCONF_URI will be Manifested (probably the same way in portage)

To further offset the problem of QA in this tree (mentioned in
"Jobuild" above), when Jobs are created/committed/uploaded on the
server (the details of that are in the next section), the whole
depgraph is validated, details about that stored as metadata, and the
Job itself is attached to **that specific revision** of the Jobtage
tree. This prevents breakages due to future changes made to the
jobuilds it depends on. If the maintainer wishes to update the
attached revision (for say a bugfix in a depending jobuild), he can
force a re-validation at anytime before a Job is accepted by a Slave.
Whenever a Slave accepts a Job, it syncs with the revision of the tree
it's attached to.

The other solution to this problem could've been to trigger a reverse
depgraph validation whenever a commit was made to the tree. The
problems with that approach are:
- Load on the server increases exponentially with jobuilds
- Raises the question of what the next action should be -- revert the
(potentially critical) commit or mark (potentially hundreds of)
jobuilds as broken?
- Makes Jobs fragile -- a job might be fine when you upload it, but
horribly broken 4 hours later.


Slaves:
--------
The slave can pull a list of Jobs that it can do from the master
server. A Job will consist of metadata about it:
http://pastebin.osuosl.org/8358 . The actual data is then gathered
from the jobuild(s), the chroot is prepared, etc etc and work begins.
Slave reports back to the master server after every jobuild is
complete with data and receives updates (if any) about the Job
(updates might consist of changing depends due to SIDEPENDs).

Obviously the Slave has to parse jobuilds. And so the concepts should
be similar to Portage. However, I am drawing inspiration from the
pkgcore[2] codebase, simplifying the extremely versatile code to suit
my needs (which is another reason for my slow progress -- it's not
easy to understand a work of art ;)


Actual Progress aka "No more hand-waving":
------------------------------------------------------
Now follows my *real* progress w.r.t the code.

I'm currently working on the slave, and am concentrating on the things
that don't depend on the part of parsing the jobuilds (have a general
idea how it's done, haven't fleshed out the details). Currently I've
implemented an OO interface (in Python of course) to a Job() object
accessed via Jobs(), a Syncer() object (jobtage), a Fetchable object
and a Fetcher (stage3 etc). Total code comes out to 167+70+38+30 =
~300 lines ;p

This week I'll start on chroot preparation and iron out the kinks in
that, followed by the Jobuild() object, the jobuild parser
(jobuild.sh), and the bridge connecting them. The #pkgcore guys are
really helpful and nice so I'll have good help for this part :)

Next week (end of the month) will (hopefully) see a working slave
which accepts Jobs from some magical source and runs them.

I'll begin work on the Master server the week after that, specifically
the backend work and the details of the communication between the
Master and Slaves. Frontend prettyfication will take place towards the
end.


1. http://www.djangobook.com/en/1.0/chapter04/ -- not the exact
format, only the idea of "Reverse Inheritance"
2. http://www.pkgcore.org/

PS: Another reason why progress is slow is because the Slave portion
has become much more sophisticated than what I had originally
intended. The original idea had (maintainer-made) executables doing
all the work (causing a steep learning curve) with the Slave just
being an API wrapper to talk to the master server. All of that work is
now shifted into the Slave and abstracted for the maintainer to use in
a familiar way.

-- 
~Nirbheek Chauhan
-- 
gentoo-soc@g.o mailing list


Replies:
Re: Progress report - AutotuA (formerly "Automate it All")
-- Eric Thibodeau
Re: Progress report - AutotuA (formerly "Automate it All")
-- Nirbheek Chauhan
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Updated Jun 17, 2009

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