Add Ubuntu 22.04 upgrade guide

docs/source/config_files.rst

@@ -233,6 +233,8 @@ To see an example repository visit
 `nix binder example <https://github.com/binder-examples/nix>`_.
 
 
+.. _dockerfile:
+
 ``Dockerfile`` - Advanced environments
 ======================================
 

docs/source/howto/breaking_changes.md

@@ -0,0 +1,26 @@
+# Deal with breaking changes in repo2docker
+
+Repo2docker occasionally has to make breaking changes in how repositories are built.
+
+## Upgrade of base image from Ubuntu 18.04 to 22.04
+
+The base image used by repo2docker was [upgraded from Ubuntu 18.04 to Ubuntu 22.04](https://github.com/jupyterhub/repo2docker/pull/1287) in version 2023.10.0 due to Ubuntu 18.04 going out of support.
+
+This is unlikely to affect you unless you are using {ref}`apt.txt <apt.txt>`.
+
+{ref}`apt.txt <apt.txt>` installs packages from the official Ubuntu package repositories, and is intrinsically tied to the Ubuntu version.
+Many packages will be available in both Ubuntu 18.04 and Ubuntu 22.04, however some may be renamed (for example if multiple incompatible versions are available).
+
+Some packages may be removed, or may not be compatible with the previous version.
+In this case you should see if your packages can be installed using a {ref}`Conda environment.yml file <environment.yml>` using either the default [conda-forge channel](https://conda-forge.org/feedstock-outputs/) or in one of the many [third-party channels](https://docs.conda.io/projects/conda/en/latest/user-guide/concepts/channels.html).
+
+Alternatively you can try installing the packages from source, using a {ref}`postBuild <postBuild>` script.
+
+As a last resort you can install an older version of repo2docker locally, build your image, push it to a public container registry such as [Docker Hub](https://hub.docker.com/), [GitHub Container Registry](https://docs.github.com/en/packages/guides/about-github-container-registry) or [quay.io](https://quay.io/), and replace your repository's repo2docker configuration with a minimal {ref}`Dockerfile <dockerfile>` containing just:
+
+```dockerfile
+FROM <registry>/<username>/<image>:<tag>
+```
+
+This image will contain a frozen version of your repository at the time the image was built.
+You will need to rebuild and push it everytime your repository is modified.

docs/source/howto/index.rst

@@ -13,6 +13,7 @@ Select from the pages listed below to get started.
    languages
    export_environment
    lab_workspaces
+   breaking_changes
    jupyterhub_images
    deploy
    base_image