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Sep 01, 2011

  1. Jérôme Petazzoni

    Handle Static and Media Assets

    We still lack the CSS required to make our admin interface look nice.
    We need to do three things here.
    
    First, we will edit ``settings.py`` to specify ``STATIC_ROOT``,
    ``STATIC_URL``, ``MEDIA_ROOT``, and ``MEDIA_URL``. Note that we
    decided to put those files in ``/home/dotcloud/data``. By convention,
    the ``data`` directory will persist across pushes. This is important:
    while you could store static assets in ``/home/dotcloud/current``
    (or one of its subdirectories), you probably don't want to store
    media (user uploaded files...) in ``current`` or ``code``, because
    those directories are wiped out at each push.
    
    The next step is to instruct Nginx to map ``/static`` and ``/media``
    to those directories in ``/home/dotcloud/data``. This is done through
    a Nginx configuration snippet. You can do many interesting things
    with custom Nginx configuration files; http://docs.dotcloud.com/guides/nginx/
    gives some details about that.
    
    The last step is to add the ``collectstatic`` management command to
    our ``postinstall`` script. Before calling it, we create the required
    directories, just in case.
    
    ..
    
    After pushing this last round of modifications, the CSS for the admin
    site (and other static assets) will be found correctly, and we have a
    very basic (but functional) Django project to build on!
    authored August 31, 2011
  2. Jérôme Petazzoni

    Create Django Superuser

    Since the ``syncdb`` command was run non-interactively, it did not
    prompt us to create a superuser, and therefore, we don't have a
    user to login.
    
    To create an admin user automatically, we will write a simple Python
    script that will use Django's environment, load the authentication
    models, create a ``User`` object, set a password, and give him
    superuser privileges.
    
    The user login will be ``admin``, and its password will be ``password``.
    Note that if the user already exists, it won't be touched. However,
    if it does not exist, it will be re-created. If you don't like this
    ``admin`` user, you should not delete it (it would be re-added each
    time you push your code) but just remove its privileges and reset its
    password, for instance.
    
    ..
    
    At this point, if we push the code, we will be able to login, but
    we still lack the CSS that will make the admin site look nicer.
    authored August 31, 2011
  3. Jérôme Petazzoni

    Automatically Call syncdb

    To make sure that the database structure is properly created, we
    want to call ``manage.py syncdb`` automatically each time we push
    our code. On the first push, this will create the Django tables;
    later, it will create new tables that might be required by new
    models you will define.
    
    To make that happen, we create a ``postinstall`` script. It is
    called automatically at the end of each push operation.
    
    ..
    
    A few remarks:
    
    * this is a shell script (hence the ``#!/bin/sh`` shebang at the
      beginning), but you can also use a Python script if you like;
    * by default, ``syncdb`` will interactively prompt you to create
      a Django superuser in the database, but we cannot interact with
      the terminal during the push process, so we disable this thanks
      to ``--noinput``.
    
    If you push the code at this point, hitting the ``/admin`` URL
    will display the login form, but we don't have a valid user yet,
    and the login form won't have the usual Django CSS since we didn't
    take care about the static assets yet.
    authored August 31, 2011
  4. Jérôme Petazzoni

    Django Admin Site

    We will now activate the Django administration application.
    Nothing is specific to DotCloud here: we just uncomment the relevant
    lines of code in ``settings.py`` and ``urls.py``.
    
    ..
    
    If we push our application now, we can go to the ``/admin`` URL,
    but since we didn't call ``syncdb`` yet, the database structure
    doesn't exist, and Django will refuse to do anything useful for us.
    authored August 31, 2011
  5. Jérôme Petazzoni

    Add Database Credentials to settings.py

    Now, we need to edit ``settings.py`` to specify the host, port, user,
    and password to connect to our database. When you deploy your application,
    these parameters are stored in the DotCloud Environment File.
    This allows you to repeat the deployment of your application
    (e.g. for staging purposes) without having to manually copy-paste
    the parameters into your settings each time.
    
    If you don't want to use the Environment File, you can retrieve the
    same information with ``dotcloud info hellodjango.db``.
    
    The Environment File is a JSON file holding a lot of information about
    our stack. It contains (among other things) our database connection
    parameters. We will load this file, and use those parameters in Django's
    settings.
    
    See http://docs.dotcloud.com/guides/environment/ for more details about
    the Environment File.
    
    ..
    
    .. note::
    
       We decided to use the ``template1`` database here. This was made
       to simplify the configuration process. If you want to use another
       database, you will have to create it manually, or to add some extra
       commands to the ``postinstall`` script shown in next sections.
    authored August 31, 2011
  6. Jérôme Petazzoni

    Add PostgreSQL Database

    It's time to add a database to our project! The first step is to tell
    DotCloud that we want a PostgreSQL server to be added to our application.
    Just edit the Build File again.
    
    ..
    
    Note that we called our database ``db``, but it could have been anything
    else, really.
    
    If you ``dotcloud push`` again, you will see that the database service
    will be created (DotCloud will notice that we added a section to the
    Build File).
    authored August 31, 2011
  7. Jérôme Petazzoni

    wsgi.py

    The ``wsgi.py`` file will bridge between the ``python`` service and our
    Django app.
    
    We need two things here:
    
    * inject the ``DJANGO_SETTINGS_MODULE`` variable into the environment,
      pointing to our project settings module;
    * setup the ``application`` callable, since that is what the DotCloud
      service will be looking for.
    
    ..
    
    We can now push our application, by running ``dotcloud push djangotutorial``
    (you can of course use any application name you like). A Python service
    will be created, the code will be deployed, and the URL of the service
    will be shown at the end of the build. If you go to this URL, you will
    see the plain and boring Django page, typical of the "just started"
    project.
    authored August 31, 2011
  8. Jérôme Petazzoni

    Django Basic Files

    Let's pretend that our Django project is called ``hellodjango``.
    We will add the essential Django files to our project.
    Actually, those files did not come out of nowhere: we just ran
    ``django-admin.py startproject hellodjango`` to generate them!
    
    .. note::
    
       The rest of the tutorial assumes that your project is in the
       ``hellodjango`` directory. If you're following those instructions
       to run your existing Django project on DotCloud, just replace
       ``hellodjango`` with the real name of your project directory,
       of course.
    authored August 31, 2011
  9. Jérôme Petazzoni

    Specifying Requirements

    A lot of Python projects use a ``requirements.txt`` file to list
    their dependencies. DotCloud detects this file, and if it exists,
    ``pip`` will be used to install the dependencies.
    
    In our case, we just need to add ``Django`` to this file.
    
    ..
    
    ``pip`` is able to install code from PyPI (just like ``easy_install``);
    but it can also install code from repositories like Git or Mercurial,
    as long as they contain a ``setup.py`` file. This is very convenient
    to install new versions of packages automatically without having to
    publish them on PyPI at each release.
    
    See http://www.pip-installer.org/en/latest/requirement-format.html for
    details about ``pip`` and the format of ``requirements.txt``.
    authored August 31, 2011
  10. Jérôme Petazzoni

    DotCloud Build File

    The DotCloud Build File, ``dotcloud.yml``, describes our stack.
    
    We will start with a single "python" service (we will add the database later).
    This service allows us to expose a WSGI-compliant web application. Django
    can do WSGI out of the box, so that's perfect for us.
    
    ..
    
    The role and syntax of the DotCloud Build File is explained in further
    detail in the documentation, at http://docs.dotcloud.com/guides/build-file/.
    authored August 31, 2011

Aug 31, 2011

  1. Jérôme Petazzoni

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    authored August 31, 2011
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