Running a server

Pydap comes with a lightweight and scalable OPeNDAP server, implemented as a WSGI application. Being a WSGI application, Pydap can run on a variety of servers, including Apache, IIS or even as a standalone Python process. It can also be seamless combined with different middleware for authentication/authorization, GZip compression, and much more.

In order to distribute your data first you need to install a proper handler, that will convert the data format to the Pydap data model.

Running standalone

If you just want to quickly test the Pydap server, you can run it as a standalone Python application using the server that comes with Python Paste:

$ paster create -t pydap myserver

To run the server just issue the command:

$ paster serve ./myserver/server.ini

This will run the server on http://localhost:8001/, serving files from ./myserver/data/. By default the server will listen only to local requests, ie, from the same machine. You can change this by editing the server.ini file; and you can also change the port number, though for ports lower than 1024 you will probably need to run the script as root.

To change the default directory listing, the help page and the HTML form, simply edit the corresponding templates in ./myserver/templates/. The HTML form template is fairly complex, since it contain some application logic and some Javascript code, so be careful to not break anything.

Running Pydap with Apache

For a robust deployment you should run Pydap with Apache, using mod_wsgi. After installing mod_wsgi, create a sandbox in a directory outside your DocumentRoot, say /var/www/pydap/, using virtualenv:

$ mkdir /var/www/pydap
$ python virtualenv.py /var/www/pydap/env

If you want the sandbox to use your system installed packages (like Numpy, e.g.) you can use the --system-site-packages flag:

$ python virtualenv.py --system-site-packages /var/www/pydap/env

Now let’s activate the sandbox and install Pydap – this way the module and its dependencies can be isolated from the system libraries:

$ source /var/www/pydap/env/bin/activate.sh
(env)$ pip install Pydap

And now we can install the basic server files:

(env)$ cd /var/www/pydap
(env)$ paster create -t pydap server

Now edit the file /var/www/pydap/server/apache/pydap.wsgi and insert the two following lines in the beginning of the file, forcing mod_wsgi to use the Python modules from the sandbox:

import site
site.addsitedir('/var/www/pydap/env/lib/python2.X/site-packages')

You’ll need to insert the correct path (including Python version) to your sandbox site-packages directory, of course. After this, your file should look like this:

import site
site.addsitedir('/var/www/pydap/env/lib/python2.X/site-packages')

import os
from paste.deploy import loadapp

config = os.path.join(os.path.dirname(__file__), '../server.ini')
application = loadapp('config:%s' % config)

Now create an entry in your Apache configuration pointing to the pydap.wsgi file you just edited. To mount the server on the URL /pydap, for example, you should configure it like this:

WSGIScriptAlias /pydap /var/www/pydap/server/apache/pydap.wsgi

<Directory /var/www/pydap/server/apache>
    Order allow,deny
    Allow from all
</Directory>

This is the file I use for the test.pydap.org virtualhost:

<VirtualHost *:80>
    ServerAdmin [email protected]
    ServerName test.pydap.org

    DocumentRoot /var/www/sites/test.pydap.org/server/data

    <Directory /var/www/sites/test.pydap.org/server/data>
        Order allow,deny
        Allow from all
    </Directory>

    WSGIScriptAlias / /var/www/sites/test.pydap.org/server/apache/pydap.wsgi

    <Directory /var/www/sites/test.pydap.org/server/apache>
        Order allow,deny
        Allow from all
    </Directory>

    ErrorLog /var/log/apache2/test.pydap.org.error.log

    # Possible values include: debug, info, notice, warn, error, crit,
    # alert, emerg.
    LogLevel warn

    CustomLog /var/log/apache2/test.pydap.org.access.log combined
    ServerSignature On
</VirtualHost>

You can find more information on the mod_wsgi configuration guide. Just remember that Pydap is a WSGI application like any other else, so any information on WSGI applications applies to it as well.

Running Pydap with uWSGI

uWSGI is a “fast, self-healing and developer/sysadmin-friendly application container server coded in pure C” that can run Pydap. This is the recommended way to run Pydap if you don’t have to integrate it with other web applications. Simply install uWSGI, follow the instructions in the last section in order to create a virtualenv and Pydap installation:

$ mkdir /var/www/pydap
$ python virtualenv.py /var/www/pydap/env
$ source /var/www/pydap/env/bin/activate.sh
(env)$ pip install Pydap uWSGI
(env)$ cd /var/www/pydap
(env)$ paster create -t pydap server

Now create a file in /etc/init/pydap.conf with the content:

description "uWSGI server for Pydap"

start on runlevel [2345]
stop on runlevel [!2345]

respawn

exec /var/www/pydap/env/bin/uwsgi \
    --http-socket 0.0.0.0:80 \
    -H /var/www/pydap/env \
    --master --processes 4 \
    --paste config:/var/www/pydap/server/server.ini

In order to make it run automatically during boot on Linux you can type:

$ sudo initctl reload-configuration