Make Podman support more prominent in the documentation

.github/workflows/test.yml

@@ -53,6 +53,8 @@ jobs:
       matrix:
         ubuntu_version: ["24.04"]
         python_version: ["3.13"]
+        container_cli:
+          - docker
         repo_type:
           - base
           - conda
@@ -68,11 +70,34 @@ jobs:
           - norun
           # Playwright test
           - ui
+        # If the item to be include would overwrite a value,
+        # it must have all the fields!
         include:
           # The earliest actions/setup-python versions depend on the runner.
           - ubuntu_version: "24.04"
             python_version: "3.10"
+            container_cli: docker
             repo_type: venv
+          # Run all tests for both Docker and Podman is expensive.
+          # We only run the "smoke" test for Podman.
+          - ubuntu_version: "24.04"
+            python_version: "3.13"
+            container_cli: podman
+            repo_type: base
+          # We are observing "no space left on device" on GitHub Actions,
+          # https://github.com/jupyterhub/repo2docker/pull/1471#issuecomment-3744990787
+          # - ubuntu_version: "24.04"
+          #   python_version: "3.13"
+          #   container_cli: podman
+          #   repo_type: conda
+          - ubuntu_version: "24.04"
+            python_version: "3.13"
+            container_cli: podman
+            repo_type: dockerfile
+          - ubuntu_version: "24.04"
+            python_version: "3.13"
+            container_cli: podman
+            repo_type: unit
 
     steps:
       - uses: actions/checkout@v6
@@ -104,6 +129,11 @@ jobs:
 
       - name: Run pytest
         run: |
+          if [ "${{ matrix.container_cli }}" = "podman" ]
+          then
+          systemctl --user start podman.socket
+          export DOCKER_HOST=unix://$(podman info --format '{{.Host.RemoteSocket.Path}}')
+          fi
           pytest --verbose --color=yes --durations=10 --cov=repo2docker tests/${{ matrix.repo_type }}
 
       - uses: codecov/codecov-action@v5

docs/source/index.md

@@ -1,15 +1,19 @@
 # Welcome to `repo2docker`'s documentation
 
+```{important}
+Despite the name, `repo2docker` can be used by container technology other than [Docker](https://docs.docker.com/engine/), for example [Podman](https://podman.io/).
+```
+
 `repo2docker` lets you **reproducibly build and run user environment container images for interactive computing and data workflows from source code repositories**. Optionally, the container image can be pushed to a Docker registry.
 
 Also, `repo2docker` is the tool used to build container images for [JupyterHub](https://jupyterhub.readthedocs.io/en/stable/) and the tool used by [BinderHub](https://binderhub.readthedocs.io) to build images on demand.
 
 ::::{grid}
 :::{grid-item-card} 🔧 Build reproducible data science environments from repositories
-Build a reproducible data science environment as a Docker image and execute code interactively. Use many [configuration files](#config-files) to control language, tools, and setup instructions.
+Build a reproducible data science environment as a container image and execute code interactively. Use many [configuration files](#config-files) to control language, tools, and setup instructions.
 :::
 :::{grid-item-card} 🚀 Deploy environments in JupyterHub or Binder
-Push environment images to a Docker registry for re-use in data science environment services like [JupyterHub](https://jupyterhub.readthedocs.io) or [a Binder instance](https://mybinder.org), or for other communities to build upon your base environment.
+Push environment images to a container registry for re-use in data science environment services like [JupyterHub](https://jupyterhub.readthedocs.io) or [a Binder instance](https://mybinder.org), or for other communities to build upon your base environment.
 :::
 :::{grid-item-card} ☁️ Host repositories in many providers
 Host repositories in: a Git server like [GitHub](https://github.com/) or [GitLab](https://gitlab.com/), an open science repository like [Zenodo](https://zenodo.org) or [Figshare](https://figshare.com), a hosted data platform like a [Dataverse installation](https://dataverse.org/), an archive like the
@@ -19,7 +23,7 @@ Host repositories in: a Git server like [GitHub](https://github.com/) or [GitLab
 
 ## What is a user environment container image and why would I build one with `repo2docker`?
 
-A **user environment container image** contains the entire software environment that a user may access from an interactive data science session. For example, it might contain many **programming languages**, **software for data analysis**, or even **content files and datasets** available to anybody that accesses that environment. Container images are built with [Docker](https://www.docker.com/), a standard open source tool for defining, building, and deploying images.
+A **user environment container image** contains the entire software environment that a user may access from an interactive data science session. For example, it might contain many **programming languages**, **software for data analysis**, or even **content files and datasets** available to anybody that accesses that environment. Container images are built in accordance with the spectifications published by the [Open Container Initiative](https://opencontainers.org/).
 
 Many data science platforms and services like [JupyterHub](https://jupyterhub.readthedocs.io) and [Binder](https://mybinder.org) launch interactive data science sessions **with a user environment container image attached**, meaning that the user gains access to whatever is in the container image. In short, this allows somebody to define and build the user image one time, in a way that users can reproducibly re-use many times.
 
@@ -43,9 +47,9 @@ repo2docker <source-repository>
 It performs these steps:
 
 1. Inspects the repository for [configuration files](#config-files). These will be used to build the environment needed to run the repository.
-2. Builds a Docker image with an environment specified in these [configuration files](#config-files).
+2. Builds a container image with an environment specified in these [configuration files](#config-files).
 3. Runs the image to let you explore the repository interactively via Jupyter notebooks, RStudio, or many other interfaces (this is optional).
-4. Pushes the images to a Docker registry so that it may be accessed remotely (this is optional).
+4. Pushes the images to a container registry so that it may be accessed remotely (this is optional).
 
 [swhid]: https://docs.softwareheritage.org/devel/swh-model/persistent-identifiers.html
 
@@ -55,7 +59,7 @@ Please report [bugs](https://github.com/jupyterhub/repo2docker/issues),
 
 ## Get started with `repo2docker`
 
-This tutorial walks you through setting up `repo2docker`, building your first environment image, and running it locally with Docker.
+This tutorial walks you through setting up `repo2docker`, building your first environment image, and running it locally with a container engine.
 
 ```{toctree}
 :maxdepth: 2

docs/source/start.md

@@ -2,47 +2,72 @@
 
 This tutorial guides you through installing `repo2docker` and building your first environment image.
 
-(install)=
+## Prerequisite
 
-## Install `repo2docker`
+### Python
 
-`repo2docker` requires Python 3.6 or above on Linux and macOS.
+`repo2docker` requires Python 3.6 or above.
 
-:::{admonition} Windows support is experimental
+### Container Engine
 
-This [article about using Windows and the WSL](https://nickjanetakis.com/blog/setting-up-docker-for-windows-and-wsl-to-work-flawlessly) (Windows Subsystem for Linux or
-Bash on Windows) provides additional information about Windows and Docker.
-:::
+`repo2docker` requires a container engine compatible with the specification published by the [Open Container Initiative](https://opencontainers.org/).
 
-### Prerequisite: Install Docker
+#### Docker
 
-Install [Docker](https://www.docker.com), as it is required to build Docker images.
-The [Community Edition](https://docs.docker.com/install/) is available for free.
+```{important}
+Only the [Docker Engine](https://docs.docker.com/engine/) is open source. [Docker Desktop](https://docs.docker.com/get-started/get-docker/) requires a license.
+```
 
-Recent versions of Docker are recommended.
+Follow [Docker's official installation steps](https://docs.docker.com/get-started/get-docker/).
 
-### Install `repo2docker` with `pip`
+#### Podman
 
-```{warning}
-The name of the package on [PyPI](https://pypi.org/) is [`jupyter-repo2docker`](https://pypi.org/project/jupyter-repo2docker/) instead of `repo2docker`.
-```
+Follow [Podman's official installation steps](https://podman.io/docs/installation).
 
-We recommend installing `repo2docker` with the `pip` tool:
+After completing the installation of Podman,
 
-```
+1. create a [listening service for Podman](https://docs.podman.io/en/latest/markdown/podman-system-service.1.html) by running
+
+   ```bash
+   systemctl --user start podman.socket
+   ```
+
+1. configure the `DOCKER_HOST` environment variable following [Podman's official procedure](https://podman-desktop.io/docs/migrating-from-docker/using-the-docker_host-environment-variable#procedure). You might want to configure the `DOCKER_HOST` environment variable to persist in your `~/.bashrc`.
+
+(install)=
+
+## Install `repo2docker`
+
+### Install `repo2docker` with `pip`
+
+It is recommend to install `repo2docker` with the `pip` tool:
+
+```bash
 python3 -m pip install jupyter-repo2docker
 ```
 
 (usage)=
 
 ## Build a repository with `repo2docker`
 
-Now that you've installed Docker and `repo2docker`, we can build a repository.
-To do so, follow these steps.
+Now that you've installed a container engine and `repo2docker`, you can build a repository.
+To do so, continue following this guide.
+
+### Start the container engine
 
-### Start Docker
+Ensure that the container engine is running.
 
-Follow the [instructions for starting Docker](https://docs.docker.com/engine/daemon/start/) to start a Docker process.
+#### Docker
+
+Follow the [offcial instructions for starting Docker](https://docs.docker.com/engine/daemon/start/).
+
+#### Podman
+
+Run
+
+```bash
+podman info
+```
 
 ### Build an image from a URL
 
@@ -55,12 +80,12 @@ jupyter-repo2docker https://github.com/binder-examples/requirements
 You'll see `repo2docker` take the following actions:
 
 1. Inspect the repository for [configuration files](#config-files). It will detect the `requirements.txt` file in the repository.
-2. Build a Docker image using the configuration files. In this case, the `requirements.txt` file will correspond to a Python environment.
+2. Build a container image using the configuration files. In this case, the `requirements.txt` file will correspond to a Python environment.
 3. Run the image to let you explore the repository interactively.
 
 Click the link provided and you'll be taken to an interactive Jupyter Notebook interface where you can run commands interactively inside the environment.
 
 ## Learn more
 
 This is a simple example building an environment image for your repository.
-To learn more about the kinds of source repositories, environments, and use-cases that repo2docker supports, see [the `repo2docker` user guide](./use/index.md).
+To learn more about the kinds of source repositories, environments, and use-cases that `repo2docker` supports, see [the `repo2docker` user guide](./use/index.md).

repo2docker/app.py

@@ -589,7 +589,11 @@ def start_container(self):
 
         docker_host = os.environ.get("DOCKER_HOST")
         if docker_host:
-            host_name = urlparse(docker_host).hostname
+            docker_host_parsed = urlparse(docker_host)
+            if docker_host_parsed.scheme == "unix":
+                host_name = "127.0.0.1"
+            else:
+                host_name = docker_host_parsed.hostname
         else:
             host_name = "127.0.0.1"
         self.hostname = host_name
@@ -621,7 +625,7 @@ def start_container(self):
                 "notebook",
                 "--ip=0.0.0.0",
                 f"--port={container_port}",
-                f"--ServerApp.custom_display_url=http://{host_name}:{host_port}",
+                f"--ServerApp.custom_display_url=http://{self.hostname}:{self.port}",
                 "--ServerApp.default_url=/lab",
             ]
         else:

repo2docker/docker.py

@@ -13,13 +13,28 @@
 from pathlib import Path
 
 from iso8601 import parse_date
-from traitlets import Dict, List, Unicode
+from traitlets import Dict, List, Unicode, default
 
 import docker
 
 from .engine import Container, ContainerEngine, Image
 from .utils import execute_cmd
 
+# The DOCKER_HOST environment variable is used by Docker to set a remote host.
+# The same DOCKER_HOST environment variable is also used
+# by the official Software Development Kit (SDK) and other libraries
+# as a way to select the socket to communicate with.
+# Because repo2docker uses the official Docker SDK,
+# Podman users MUST configure the DOCKER_HOST environment variable.
+DOCKER_HOST = os.getenv("DOCKER_HOST")
+# It is possible for a user to create a Podman socket
+# that does not include the string "podman"
+# but expect the string "podman" is good enough for repo2docker use case.
+if DOCKER_HOST is not None and DOCKER_HOST.find("podman") != -1:
+    DOCKER_CLI = "podman"
+else:
+    DOCKER_CLI = "docker"
+
 
 class DockerContainer(Container):
     def __init__(self, container):
@@ -66,6 +81,42 @@ class DockerEngine(ContainerEngine):
 
     string_output = True
 
+    _container_cli = None
+
+    @property
+    def container_cli(self):
+        if self._container_cli is not None:
+            return self._container_cli
+
+        cli = DOCKER_CLI
+
+        cli_version_call = [cli, "version"]
+        try:
+            docker_version = subprocess.run(
+                cli_version_call, stdout=subprocess.DEVNULL, check=True
+            )
+        except (subprocess.CalledProcessError, OSError) as e:
+            raise RuntimeError(
+                f"The {cli} commandline client must be installed: {e}"
+            ) from None
+
+        # docker buildx is based in a plugin that might not be installed
+        # https://github.com/docker/buildx
+        #
+        # podman buildx command is an alias of podman build.
+        # Not all buildx build features are available in Podman.
+        cli_buildx_version_call = [cli, "buildx", "version"]
+        try:
+            docker_buildx_version = subprocess.run(
+                cli_buildx_version_call, stdout=subprocess.DEVNULL, check=True
+            )
+        except (subprocess.CalledProcessError, OSError) as e:
+            raise RuntimeError(f"The buildx plugin must be installed: {e}") from None
+
+        self._container_cli = cli
+
+        return self._container_cli
+
     extra_init_args = Dict(
         {},
         help="""
@@ -105,16 +156,7 @@ def build(
         platform=None,
         **kwargs,
     ):
-        if not shutil.which("docker"):
-            raise RuntimeError("The docker commandline client must be installed")
-
-        # docker buildx is based in a plugin that might not be installed
-        # https://github.com/docker/buildx
-        docker_buildx_version = subprocess.run(["docker", "buildx", "version"])
-        if docker_buildx_version.returncode:
-            raise RuntimeError("The docker buildx plugin must be installed")
-
-        args = ["docker", "buildx", "build", "--progress", "plain"]
+        args = [self.container_cli, "buildx", "build", "--progress", "plain"]
         if load:
             if push:
                 raise ValueError(
@@ -171,14 +213,22 @@ def inspect_image(self, image):
         Return image configuration if it exists, otherwise None
         """
         proc = subprocess.run(
-            ["docker", "image", "inspect", image], capture_output=True
+            [self.container_cli, "image", "inspect", image], capture_output=True
         )
 
         if proc.returncode != 0:
             return None
 
         config = json.loads(proc.stdout.decode())[0]
-        return Image(tags=config["RepoTags"], config=config["Config"])
+        tags = config["RepoTags"]
+        oci_image_configuration = config["Config"]
+
+        # WorkingDir is optional but docker always include it.
+        # https://github.com/containers/podman/discussions/27313
+        if "WorkingDir" not in oci_image_configuration:
+            oci_image_configuration["WorkingDir"] = ""
+
+        return Image(tags=tags, config=oci_image_configuration)
 
     @contextmanager
     def docker_login(self, username, password, registry):
@@ -200,7 +250,7 @@ def docker_login(self, username, password, registry):
             try:
                 subprocess.run(
                     [
-                        "docker",
+                        self.container_cli,
                         "login",
                         "--username",
                         username,

tests/conftest.py

@@ -27,10 +27,13 @@
 import requests
 import yaml
 
+import docker
 from repo2docker.__main__ import make_r2d
 
 TESTS_DIR = os.path.abspath(os.path.dirname(__file__))
 
+DOCKER_CLIENT = client = docker.from_env()
+
 
 def pytest_collect_file(parent, file_path):
     if file_path.name == "verify":
@@ -90,6 +93,11 @@ def build_noop():
             # stop the container
             container.stop()
             app.wait_for_container(container)
+            try:
+                container.remove()
+            except:
+                pass
+            DOCKER_CLIENT.images.remove(image=app.output_image_spec)
 
     return test