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.

  • 30 minutes build time

  • 7GB of memory

  • 4 concurrent builds

If you are having trouble with your documentation builds, you can reach our support at support@readthedocs.com.

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 pin the version of Sphinx or Mkdocs you want us to use. You can do this the same way other dependencies are specified. 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:

Table 1 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

If you want to learn more about how the build environment works as a low level, you can read about it in our Build Environments docs.

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 I Need Secrets (or Environment Variables) in my Build.

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.