repo2docker/docs/source/config_files.rst

.. _config-files:

===================
Configuration Files
===================

``repo2docker`` looks for configuration files in the repository being built
to determine how to build it. In general, ``repo2docker`` uses the same
configuration files as other software installation tools,
rather than creating new custom configuration files.

A number of ``repo2docker`` configuration files can be combined to compose more
complex setups.

The `binder examples <https://github.com/binder-examples>`_ organization on
GitHub contains a list of sample repositories for common configurations
that ``repo2docker`` can build with various configuration files such as
Python and R installation in a repository.

Below is a list of supported configuration files (roughly in the order of build priority):

.. contents::
   :local:
   :depth: 1


.. _environment.yml:

``environment.yml`` - Install a Python environment
==================================================

``environment.yml`` is the standard configuration file used by `conda <https://conda.io>`_
that lets you install any kind of package,
including Python, R, and C/C++ packages.

.. note::

   You can install files from pip in your ``environment.yml`` as well.
   For example, see the `binder-examples environment.yml
   <https://github.com/binder-examples/python-conda_pip/blob/master/environment.yml>`_
   file.

You can also specify which Python version to install in your built environment
with ``environment.yml``. By default, ``repo2docker`` installs
|default_python| with your ``environment.yml`` unless you include the version of
Python in this file.  ``conda`` supports all versions of Python,
though ``repo2docker`` support is best with Python 3.7, 3.6, 3.5 and 2.7.

.. warning::
   If you include a Python version in a ``runtime.txt`` file in addition to your
   ``environment.yml``, your ``runtime.txt`` will be ignored.


.. _requirements.txt:

``requirements.txt`` - Install a Python environment
===================================================

This specifies a list of Python packages that should be installed in your
environment. Our
`requirements.txt example <https://github.com/binder-examples/requirements/blob/master/requirements.txt>`_
on GitHub shows a typical requirements file.


.. _setup.py:

``setup.py`` - Install Python packages
======================================

To install your repository like a Python package, you may include a
``setup.py`` file. repo2docker installs ``setup.py`` files by running
``pip install -e .``.


.. _REQUIRE:

``REQUIRE`` - Install a Julia environment
=========================================

This specifies a list of Julia packages. To see an example of a
Julia repository with ``REQUIRE`` and ``environment.yml``,
visit `binder-examples/julia-python <https://github.com/binder-examples/julia-python>`_.


.. _install.R:

``install.R`` - Install an R/RStudio environment
================================================

This is used to install R libraries pinned to a specific snapshot on
`MRAN <https://mran.microsoft.com/documents/rro/reproducibility>`_.
To set the date of the snapshot add a runtime.txt_.
For an example ``install.R`` file, visit our `example install.R file <https://github.com/binder-examples/r/blob/master/install.R>`_.


.. _apt.txt:

``apt.txt`` - Install packages with apt-get
===========================================

A list of Debian packages that should be installed. The base image used is usually the latest released
version of Ubuntu.

We use ``apt.txt``, for example, to install LaTeX in our
`example apt.txt for LaTeX <https://github.com/binder-examples/latex/blob/master/apt.txt>`_.


.. _DESCRIPTION:

``DESCRIPTION`` - Install an R package
======================================

To install your repository like an R package, you may include a
``DESCRIPTION`` file. repo2docker installs the package and dependencies
from the ``DESCRIPTION`` by running ``devtools:install_git(".")``.

You also need to have a ``runtime.txt`` file that is formatted as
``r-<YYYY>-<MM>-<DD>``, where YYYY-MM-DD is a snapshot of MRAN that will be
used for your R installation.


.. _manifest.xml:

``manifest.xml`` - Install Stencila
===================================

`Stencila <https://stenci.la/>`_ is an open source office suite for reproducible research.
It is powered by the open file format `Dar <https://github.com/substance/dar>`_.

If your repository contains a Stencila document, repo2docker detects it based on the file ``manifest.xml``.
The required `execution contexts <https://stenci.la/learn/intro.html>`_ are extracted from a Dar article (i.e.
files named ``*.jats.xml``).

You may also have a ``runtime.txt`` and/or an ``install.R`` to manually configure your R installation.

To see example repositories, visit our
`Stencila with R <https://github.com/binder-examples/stencila-r/>`_ and
`Stencila with Python <https://github.com/binder-examples/stencila-py>`_ examples.


.. _postBuild:

``postBuild`` - Run code after installing the environment
=========================================================

A script that can contain arbitrary commands to be run after the whole repository has been built. If you
want this to be a shell script, make sure the first line is ``#!/bin/bash``.

An example use-case of ``postBuild`` file is JupyterLab's demo on mybinder.org.
It uses a ``postBuild`` file in a folder called ``binder`` to `prepare
their demo for binder <https://github.com/jupyterlab/jupyterlab-demo/blob/master/binder/postBuild>`_.


.. _start:

``start`` - Run code before the user sessions starts
====================================================

A script that can contain simple commands to be run at runtime (as an
`ENTRYPOINT <https://docs.docker.com/engine/reference/builder/#entrypoint>`_
to the docker container). If you want this to be a shell script, make sure the
first line is ``#!/bin/bash``. The last line must be ``exec "$@"``
equivalent.

Use this to set environment variables that software installed in your container
expects to be set. This script is executed each time your binder is started and
should at most take a few seconds to run.

If you only need to run things once during the build phase use :ref:`postBuild`.


.. TODO: Discuss runtime limits, best practices, etc.

.. _runtime.txt:

``runtime.txt`` - Specifying runtimes
=====================================

Sometimes you want to specify the version of the runtime
(e.g. the version of Python or R),
but the environment specification format don't let you specify this information
(e.g. requirements.txt or install.R).
For these cases, we have a special file, ``runtime.txt``.

.. note::

   ``runtime.txt`` is only supported when used with environment specifications
   that do not already support specifying the runtime
   (e.g. when using ``environment.yml`` for conda or ``REQUIRE`` for Julia,
   ``runtime.txt`` will be ignored).

To use python-2.7: add ``python-2.7`` in runtime.txt file.
The repository will run in an env with
Python 2 installed. To see a full example repository, visit our
`Python2 example <https://github.com/binder-examples/python2_runtime/blob/master/runtime.txt>`_.

repo2docker uses R libraries pinned to a specific snapshot on
`MRAN <https://mran.microsoft.com/documents/rro/reproducibility>`_.
You need to have a ``runtime.txt`` file that is formatted as
``r-<YYYY>-<MM>-<DD>``, where YYYY-MM-DD is a snapshot at MRAN that will be
used for installing libraries.

To see an example R repository, visit our `R
example in binder-examples <https://github.com/binder-examples/r/blob/master/runtime.txt>`_.


.. _default.nix:

``default.nix`` - the nix package manager
=========================================

Specify packages to be installed by the `nix package manager <https://github.com/NixOS/nixpkgs>`_.
When you use this config file all other configuration files (like ``requirements.txt``)
that specify packages are ignored. When using ``nix`` you have to specify all
packages and dependencies explicitly, including the Jupyter notebook package that
repo2docker expects to be installed. If you do not install Jupyter explicitly
repo2docker will no be able to start your container.

`nix-shell <https://nixos.org/nix/manual/#sec-nix-shell>`_ is used to evaluate
a ``nix`` expression written in a ``default.nix`` file. Make sure to
`pin your nixpkgs <https://discourse.nixos.org/t/nixops-pinning-nixpkgs/734>`_
to produce a reproducible environment.

To see an example repository visit
`nix binder example <https://github.com/binder-examples/nix>`_.


``Dockerfile`` - Advanced environments
======================================

In the majority of cases, providing your own Dockerfile is not necessary as the base
images provide core functionality, compact image sizes, and efficient builds. We recommend
trying the other configuration files before deciding to use your own Dockerfile.

With Dockerfiles, a regular Docker build will be performed.

.. note::
    If a Dockerfile is present, all other configuration files will be ignored.

See the `Advanced Binder Documentation <https://mybinder.readthedocs.io/en/latest/tutorials/dockerfile.html>`_ for
best-practices with Dockerfiles.