Nova.astrometry.net orientation

Getting started:

  • you’ll need an account on astrometry.net (for svn), and to have your ssh public key added to the authorized_keys for nova@oven.cosmo.fas.nyu.edu
  • can you ssh in as nova@oven.cosmo.fas.nyu.edu?
  • can you svn checkout the Astrometry.net code? (see svn checkout the Astrometry.net code)

Nova

As for the nova website code: if you svn checked out the Astrometry.net code, you should have a net directory – that’s where the server-side code that runs the nova.astrometry.net site lives. It’s written in python using the Django framework, which provides nice web and database routines.

We actually run three copies of the nova website:

  • supernova.astrometry.net – “trunk”, for testing and development
  • staging.astrometry.net – test-flight area when we think we have a releaseable version.
  • nova.astrometry.net – the production site. This runs off an “svn tagged” version – not trunk

The web sites are run via the apache web server. You probably won’t have to deal with that side at all. Each one runs out of a directory within nova@oven‘s home directory. They’re called (this may shock you), “supernova”, “staging”, and “nova”. There is a server-side process that has to be running in order for the web site to do anything with images that people submit. That’s called process_submissions.py (you can see the code in net/process_submissions.py), and for each site we run it in a screen. screen is an old-school utility that lets you create a “virtual terminal” that you can “attach” to and “detach” from. It’s a handy way of keeping a program running on a server when you’re not logged in. Anyway, if you’re logged in as nova@oven you can do:

screen -ls

to see the currently-running screens;

nova@oven:~$ screen -ls
There are screens on:
    20579.supernova (03/18/2012 08:15:43 PM)        (Detached)
    27698.nova      (03/14/2012 06:11:25 PM)        (Detached)
2 Sockets in /var/run/screen/S-nova.

which says there are two screens, supernova and nova.

You can “attach” or “rejoin” with:

screen -R supernova

and you should see “process_submissions.py” doing its thing:

Checking for new Submissions
Found 0 unstarted submissions
Checking for UserImages without Jobs
Found 0 userimages without Jobs
Submissions running: 0
Jobs running: 0

anyway, to “detach” from that screen, do:

ctrl-a d

Ok, so coming back to the code, let’s find out where the data live.

Each site has a settings file. So, as nova@oven:

nova@oven:~$ cd supernova/net
nova@oven:~/supernova/net$ ls -l settings.py
lrwxrwxrwx 1 nova nova 21 2011-06-09 19:16 settings.py -> settings_supernova.py

So in the supernova directory, settings.py is a symlink to settings_supernova.py . Let’s look in there:

# settings_supernova.py
from settings_common import *

DATABASES['default']['NAME'] = 'an-supernova'

LOGGING['loggers']['django.request']['level'] = 'WARN'

SESSION_COOKIE_NAME = 'SupernovaAstrometrySession'

# Used in process_submissions
ssh_solver_config = 'an-supernova'
sitename = 'supernova'

oh, it hardly has anything. But at the top it imports everything from settigs_common.py. Looking there, we see:

...
WEB_DIR = os.path.dirname(astrometry.net.__file__) + '/'
DATADIR = os.path.join(WEB_DIR, 'data')
...

so it figures out the directory it is currently running in based on the location of the astrometry.net python package (WEB_DIR), which for supernova will be:

/home/nova/supernova/net

and the DATADIR is that + data. If you look in that data directory, you’ll see:

nova@oven:~/supernova/net$ ls data
00  08  12  19  25  2c  34  3a  41  49  50  57  60  67  6f  74  7e  8a  91  9a  a3  ad  b4  bf  c6  d4  da  e0  eb  f5
03  0b  14  1a  27  2e  36  3b  43  4a  52  59  62  6a  70  75  85  8b  92  9d  a6  ae  b5  c0  c7  d5  db  e2  ef  fa
04  0c  15  20  29  2f  37  3d  44  4b  53  5a  63  6b  71  76  86  8c  94  9e  aa  b0  b7  c3  ca  d6  dc  e4  f0  fb
06  0d  16  23  2a  32  38  3e  45  4c  55  5b  65  6c  72  79  87  8d  98  9f  ab  b1  b9  c4  cb  d7  dd  e6  f2  fd
07  11  18  24  2b  33  39  3f  46  4e  56  5e  66  6d  73  7a  89  8f  99  a2  ac  b3  ba  c5  d1  d8  de  e9  f3  ff

ok, a bunch of directories. What’s in them?

nova@oven:~/supernova/net$ find data/00
data/00
data/00/32
data/00/32/84
data/00/32/84/00328489cbdfce1a99ebbf1078c95669e39fa8a7
nova@oven:~/supernova/net$ file data/00/32/84/00328489cbdfce1a99ebbf1078c95669e39fa8a7
data/00/32/84/00328489cbdfce1a99ebbf1078c95669e39fa8a7: JPEG image data, JFIF standard 1.01

And check this out:

nova@oven:~/supernova/net$ sha1sum data/00/32/84/00328489cbdfce1a99ebbf1078c95669e39fa8a7
00328489cbdfce1a99ebbf1078c95669e39fa8a7  data/00/32/84/00328489cbdfce1a99ebbf1078c95669e39fa8a7

So the files are named according to a cryptographic hash of their contents (SHA-1), and sorted into subdirectories according to the first three pairs of hexadecimal digits:

AA/BB/CC/AABBCC....

(We sort them into subdirectories like that to avoid having a huge number of files in a single directory.)

Running on a local machine (your laptop, say)

Prerequisites:

Once you’ve got the code checked out, you need to symlink one of the settings_*.py files to settings.py:

ln -s settings_test.py settings.py

for local testing, settings_test.py is the best bet, since it uses a local sqlite3 database rather than a real external database.

Initialize the database:

python manage.py syncdb
python manage.py migrate

Then you can run the Django web server by running:

python manage.py runserver

And then go to: http://localhost:8000

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