Using docker to build Read the Docs

The Problem

An old side-project was using an out-of-date version of IdentityServer4 (2.0.0). The project was mainly a learning project, so before jumping to the latest, I wanted to see what changed between 2.0.0 and 2.5.4.

Unfortunately, the documentation at didn't have anything from the version 2 days. So I decided to build them myself in docker.

Building the docs in docker

IdentityServer uses "Read the Docs", which is built with Sphinx document generator. To make things slightly simpler, there are already Sphinx docker images up on docker Hub. Even better, they include instructions on how to mount a volume and perform a build. So I tried it.

First things first, cloning the repo and checkout out the version I wanted to build:

git clone
cd IdentityServer4
git checkout tags/2.5.4 -b tag_2_5_4

Missing dependencies

Taking the command directly from docker hub I hit a snag:

 docker run --rm -v C:\Play\Repos\IdentityServer4\docs:/docs sphinxdoc/sphinx make html

 Running Sphinx v3.2.1

Configuration error:
There is a programmable error in your configuration file:

Traceback (most recent call last):
  File "/usr/local/lib/python3.8/site-packages/sphinx/", line 319, in eval_config_file
    execfile_(filename, namespace)
  File "/usr/local/lib/python3.8/site-packages/sphinx/util/", line 89, in execfile_
    exec(code, _globals)
  File "/docs/", line 139, in <module>
    import sphinx_rtd_theme
ModuleNotFoundError: No module named 'sphinx_rtd_theme'
make: *** [Makefile:53: html] Error 2

As you can see from the highlighted line above, the image was missing a module needed. That type of thing must happen a lot, as the docker hub site includes a "tips" section on how to build your own image.

Building your own image

Following the tip, I created a Dockerfile with the following contents:

FROM sphinxdoc/sphinx

RUN pip install sphinx_rtd_theme

Built my image:

docker build -t "sphinxdocs" .

And ran the same command, but this time with my image:

docker run --rm -v C:\Play\Repos\IdentityServer4\docs:/docs sphinxdocs make html


I won't include all the output as it's long, but once that's finished, you should have a _build\html\index.html file in the docs directory containing the IdentityServer documentation as per 2.5.4.

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