# 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 `pip install -e .` 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 serves WSGI applications over HTTP.

Kallithea itself is not serving HTTP (or HTTPS); that is the web server’s responsibility. Kallithea does however need to know its own user facing URL (protocol, address, port and path) for each HTTP request. Kallithea will usually use its own HTML/cookie based authentication but can also be configured to use web server authentication.

There are several web server options:

- Kallithea uses the Paste tool as command line interface. Paste provides `paster serve` as a convenient way to launch a Python WSGI / web server from the command line. That is perfect for development and evaluation. Actual use in production might have different requirements and need extra work to make it manageable as a scalable system service.

  Paste comes with its own built-in web server but Kallithea defaults to use Waitress. Gunicorn is also an option. These web servers have different limited feature sets.

  The web server used by `paster` is configured in the `.ini` file passed to it. 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.

- uWSGI is also a full web server with built-in WSGI module.

- IIS can also server WSGI applications directly using isapi-wsgi.

- A reverse HTTP proxy can be put in front of another web server which has WSGI support. Such a layered setup can be complex but might in some cases be the right option, for example to standardize on one internet-facing web server, to add encryption or special authentication or for other security reasons, to provide caching of static files, or to provide load balancing or fail-over. Nginx, Varnish and HAProxy are often used for this purpose, often in front of a `paster` server that somehow is wrapped as a service.

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 dynamically generated pages from a 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.