Build Process

Every documentation build has limited resources. Our current build limits are:

  • 15 minutes build time

  • 3GB of memory

  • 2 concurrent builds

We can increase build limits on a per-project basis. Send an email to support@readthedocs.org providing a good reason why your documentation needs more resources.

If your business is hitting build limits hosting documentation on Read the Docs, please consider Read the Docs for Business which has much higher build resources.

Understanding what’s going on

Understanding how Read the Docs builds your project will help you with debugging the problems you have with the site. It should also allow you to take advantage of certain things that happen during the build process.

The first step of the process is that we check out your code from the repository you have given us. If the code is already checked out, we update the copy to the branch that you have specified in your project’s configuration.

Then we build the proper backend code for the type of documentation you’ve selected, this is done inside a Docker container.

At this point, if you need extra requirements, or even install your own package in the virtual environment to build your documentation, you can use a Configuration File.

When we build your Sphinx documentation, we run sphinx-build -b <format> . _build/<format> We also create pdf’s and ePub’s automatically based on your project. For MkDocs, we run mkdocs build.

Once these files are built, they are deployed to our file hosting backend and will be visible to users.

An example in code:

update_docs_from_vcs(version)
config = get_config(project)
if config.python.install.method.pip:
    run('pip install .')
if config.python.install.requirement:
    run('pip install -r %s' % config.python.install.requirement)
build_docs(version)
deploy_docs(version)

Note

Regardless of whether you build your docs with Sphinx or MkDocs, we recommend you pinning the version of Sphinx or Mkdocs you want us to use. Some examples of pinning versions might be sphinx<2.0 or mkdocs>=1.0.

Build environment

The Sphinx and Mkdocs builders set the following RTD-specific environment variables when building your documentation:

Environment Variables

Environment variable

Description

Example value

READTHEDOCS

Whether the build is running inside RTD

True

READTHEDOCS_VERSION

The RTD name of the version which is being built

latest

READTHEDOCS_PROJECT

The RTD slug of the project which is being built

my-example-project

READTHEDOCS_LANGUAGE

The RTD language slug of the project which is being built

en

Tip

In case extra environment variables are needed to the build process (like secrets, tokens, etc), you can add them going to Admin > Environment Variables in your project. See Environment Variables.

Docker images

The build process is executed inside Docker containers, by default the image used is readthedocs/build:latest, but you can change that using a Configuration File.

You can see the current Docker build images that we use in our docker repository. Docker Hub also shows the latest set of images that have been built.

Default versions of dependencies

Read the Docs supports two tools to build your documentation: Sphinx and MkDocs. In order to provide several features, Read the Docs injects or modifies some content while building your docs.

In particular, if you don’t specify the dependencies of your project, we install some of them on your behalf. In the past we used to pin these dependencies to a specific version and update them after some time, but doing so would break some builds and make it more difficult for new projects to use new versions. For this reason, we are now installing their latest version by default.

Note

In order to keep your builds reproducible, it’s highly recommended declaring its dependencies and versions explicitly. See Reproducible Builds.

External dependencies

Python

These are the dependencies that are installed by default when using a Python environment:

Sphinx:

Projects created before Oct 20, 2020 use 1.8.x. New projects use the latest version.

Mkdocs:

Projects created before April 3, 2019 (April 23, 2019 for Read the Docs for Business) use 0.17.3. Projects created before March 9, 2021 use 1.0.4. New projects use the latest version.

sphinx-rtd-theme:

Projects created before October 20, 2020 (January 21, 2021 for Read the Docs for Business) use 0.4.3. New projects use the latest version.

pip:

Latest version by default.

setuptools:

58.2.0 or older.

mock:

1.0.1 (could be removed in the future).

pillow:

5.4.1 (could be removed in the future).

alabaster:

0.7.x (could be removed in the future).

commonmark:

0.8.1 (could be removed in the future).

recommonmark:

0.5.0 (could be removed in the future).

Conda

These are the dependencies that are installed by default when using a Conda environment:

Conda:

Miniconda2 4.6.14 (could be updated in the future to use the latest version by default).

Mkdocs:

Latest version by default installed via conda.

Sphinx:

Latest version by default installed via conda.

sphinx-rtd-theme:

Latest version by default installed via conda.

mock:

Latest version by default installed via pip (could be removed in the future).

pillow:

Latest version by default installed via pip (could be removed in the future).

recommonmark:

Latest version by default installed via conda (could be removed in the future).

Internal dependencies

Internal dependencies are needed to integrate your docs with Read the Docs. We guarantee that these dependencies will work with all current supported versions of our tools, you don’t need to specify them in your requirements.