Why Rez doc page

docs/source/index.rst

@@ -11,6 +11,7 @@ Welcome to rez's documentation!
    :caption: General
    :hidden:
 
+   why_rez
    installation
    getting_started
    basic_concepts

docs/source/why_rez.rst

@@ -0,0 +1,101 @@
+=======
+Why Rez
+=======
+
+What is Rez
+===========
+
+Rez v1 was originally built in 2011 by Allan Johns and was open-sourced in 2013.
+
+It was with VFX/Animation workflows in mind, where different productions can have non-homogenous package
+requests and shared filesystems are the norm.
+
+Rez is both a package manager and an environment manager.
+
+Package Manager
+---------------
+
+A package manager is a tool that helps keep track of an application's dependencies. Package managers provide
+often communicate with package repositories to install, update and remove packages on a computer.
+
+
+Environment Manager
+-------------------
+
+A runtime environment manager is a tool that allows users to easily control what a shell created environment
+will look like. This primarily takes shape by defining environment variables that will then be used by
+applications that are launched from the created shell.
+
+
+What Rez is not
+===============
+Rez is not a configuration system. It does not and should not have any knowledge as to the content of a user's
+package requests.
+
+In VFX/Animation for example, a common problem is that different projects or "shows" may need to use different
+versions of software/tools. This is especially problematic with long-standing productions such as feature films.
+
+Let's say there are two shows in production, show1 that should use Autodesk Maya 2018, and show2 that should use
+Maya 2019. The mechanism that stores and retrieves this configuration information is the configuration system.
+
+This configuration could commonly be stored in a database, and it would be tedious and error-prone to force
+non-technical artists to lookup this information and write Rez requests themselves.
+
+For this reason, it's common that the more technical folks of the studio would want to build a CLI or GUI "launcher"
+to expose to the less technical artists of the studio that would allow them to select which project they are working
+on, and perhaps which DCC tool they want to use, and the launcher will automatically formulate the Rez request.
+
+For example, a hypothetical CLI launcher like so:
+
+.. code-block:: console
+
+    usage: studio_launcher.py [-h] [-p PROJECT] dcc
+
+    A simple CLI launcher.
+
+    positional arguments:
+      dcc                       DCC tool to launch
+
+    options:
+      -h, --help                show this help message and exit
+      -p, --project PROJECT     The name of the project
+
+This launcher would know to communicate with the configuration system in order to lookup which version of the DCC
+to use and would also request any other packages that are needed (such as proprietary workflow tools).
+
+Alternatives to Rez
+===================
+
+Package Managers
+----------------
+
+`pip <https://packaging.python.org/en/latest/key_projects/#pip>`_
+
+Environment Managers
+--------------------
+`venv <https://packaging.python.org/en/latest/key_projects/#venv>`_
+
+`virtualenv <https://packaging.python.org/en/latest/key_projects/#virtualenv>`_
+
+Package and Environment Managers
+--------------------------------
+`conda <https://packaging.python.org/en/latest/key_projects/#conda>`_
+
+Conda was primarily created to solve packaging problems in the Python ecosystem, but is not Python specific.
+Conda creates persistent, on-disk environments while Rez creates in-memory ephemeral environments. Rez doesn't
+have to local install packages to work (but it can with the package caching feature), where Conda does.
+
+This feature of Rez is very useful is VFX/Animation where "work" is done on render farm machines whose disk space is
+often quite limited. Shared filesystems are common in VFX/Animation, which means they are often configured to be
+accessed very quickly. Due to this, Rez is very fast.
+
+Conda *can* create environments on shared filesystems, but
+there would be lots of caveats and hidden dragons.
+
+`spack <https://packaging.python.org/en/latest/key_projects/#spack>`_
+
+`Conan <https://docs.conan.io/2/>`_
+
+`SPK <https://getspk.io/>`_
+
+