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+.. _overview:
+
+=====================
+Installation Overview
+=====================
+
+
+Some overview and some details that can help understanding the options when
+installing Kallithea.
+
+
+Python Environment
+------------------
+
+**Kallithea** is written entirely in Python_ and requires Python version
+2.6 or higher. Python 3.x is currently not supported.
+
+Given a Python installation, there are different ways of providing the
+environment for running Python applications. Each of them pretty much
+corresponds to a ``site-packages`` directory somewhere where packages can be
+installed.
+
+Kallithea itself can be run from source or be installed, but even when running
+from source, there are some dependencies that must be installed in the Python
+environment used for running Kallithea.
+
+- Packages *could* be installed in Python's ``site-packages`` directory ... but
+  that would require running pip_ as root and it would be hard to uninstall or
+  upgrade and is probably not a good idea unless using a package manager.
+
+- Packages could also be installed in ``~/.local`` ... but that is probably
+  only a good idea if using a dedicated user per application or instance.
+
+- Finally, it can be installed in a virtualenv_. That is a very lightweight
+  "container" where each Kallithea instance can get its own dedicated and
+  self-contained virtual environment.
+
+We recommend using virtualenv for installing Kallithea.
+
+
+Installation Methods
+--------------------
+
+Kallithea must be installed on a server. Kallithea is installed in a Python
+environment so it can use packages that are installed there and make itself
+available for other packages.
+
+Two different cases will pretty much cover the options for how it can be
+installed.
+
+- The Kallithea source repository can be cloned and used - it is kept stable and
+  can be used in production. The Kallithea maintainers use the development
+  branch in production. The advantage of installation from source and regularly
+  updating it is that you take advantage of the most recent improvements. Using
+  it directly from a DVCS also means that it is easy to track local customizations.
+
+  Running ``setup.py develop`` in the source will use pip to install the
+  necessary dependencies in the Python environment and create a
+  ``.../site-packages/Kallithea.egg-link`` file there that points at the Kallithea
+  source.
+
+- Kallithea can also be installed from ready-made packages using a package manager.
+  The official released versions are available on PyPI_ and can be downloaded and
+  installed with all dependencies using ``pip install kallithea``.
+
+  With this method, Kallithea is installed in the Python environment as any
+  other package, usually as a ``.../site-packages/Kallithea-X-py2.7.egg/``
+  directory with Python files and everything else that is needed.
+
+  (``pip install kallithea`` from a source tree will do pretty much the same
+  but build the Kallithea package itself locally instead of downloading it.)
+
+
+Web Server
+----------
+
+Kallithea is (primarily) a WSGI_ application that must be run from a web
+server that expose WSGI as HTTP.
+
+- Kallithea uses the Paste_ tool for some admin tasks. Paste provides ``paste
+  serve`` as a convenient way to launch Python WSGI / web servers.
+  This method is perfect for development but *can* also be used for production.
+
+  ``paste`` is a command line tool. Using it in production requires some way to
+  wrap it as a managable service.
+
+  Paste come with its own web server but Kallithea defaults to use Waitress_.
+  Gunicorn_ is also an option. These web servers have different limited feature
+  sets.
+
+  It is also common/mandatory to put another web server or (reverse) proxy in
+  front of these Python web servers. Nginx_ is a common choice. This simple
+  setup will thus often end up being quite complex.
+
+  The configuration of which web server to use is in the ini file passed to
+  ``paste``. The entry point for the WSGI application is configured in
+  ``setup.py`` as ``kallithea.config.middleware:make_app``.
+
+- `Apache httpd`_ can serve WSGI applications directly using mod_wsgi_ and a
+  simple Python file with the necessary configuration. This is a good option if
+  Apache is an option.
+
+- IIS_ can also server WSGI applications directly using isapi-wsgi_.
+
+- UWSGI_ is also an option.
+
+The best option depends on what you are familiar with and the requirements for
+performance and stability. Also, keep in mind that Kallithea mainly is serving
+custom data generated from relatively slow Python process. Kallithea is also
+often used inside organizations with a limited amount of users and thus no
+continuous hammering from the internet.
+
+
+.. _Python: http://www.python.org/
+.. _Gunicorn: http://gunicorn.org/
+.. _Waitress: http://waitress.readthedocs.org/en/latest/
+.. _virtualenv: http://pypi.python.org/pypi/virtualenv
+.. _Paste: http://pythonpaste.org/
+.. _PyPI: https://pypi.python.org/pypi
+.. _Apache httpd: http://httpd.apache.org/
+.. _mod_wsgi: https://code.google.com/p/modwsgi/
+.. _isapi-wsgi: https://github.com/hexdump42/isapi-wsgi
+.. _UWSGI: https://uwsgi-docs.readthedocs.org/en/latest/
+.. _nginx: http://nginx.org/en/
+.. _iis: http://en.wikipedia.org/wiki/Internet_Information_Services
+.. _pip: http://en.wikipedia.org/wiki/Pip_%28package_manager%29
+.. _WSGI: http://en.wikipedia.org/wiki/Web_Server_Gateway_Interface
+.. _pylons: http://www.pylonsproject.org/