add how to build flower docker images locally docs

doc/source/contributor-how-to-build-docker-images.rst

@@ -0,0 +1,103 @@
+How to build Docker Flower images locally
+=========================================
+
+Flower provides pre-made docker images on `Docker Hub <https://hub.docker.com/r/flwr/server/tags>`_
+that include all necessary dependencies for running the server. You can also build your own custom
+docker images from scratch with a different version of Python or Ubuntu if that is what you need.
+In this guide, we will explain what images exist and how to build them locally.
+
+Before we can start, we need to meet a few prerequisites in our local development environment.
+
+1. Clone the flower repository.
+
+.. code-block:: bash
+
+  $ git clone https://github.com/adap/flower.git && cd flower
+
+2. Verify the Docker daemon is running.
+
+Please follow the first section on
+`Run Flower in Docker <https://flower.dev/docs/framework/how-to-run-flower-in-docker>`_
+which covers this step in more detail.
+
+Currently, Flower provides two images, a base image and a server image. There will also be a client
+image soon. The base image, as the name suggests, contains basic dependencies that both the server
+and the client need. This includes system dependencies, Python and Python tools. The server image is
+based on the base image, but it additionally installs the Flower server using ``pip``.
+
+Building the base image
+-----------------------
+
+.. list-table::
+   :widths: 25 50 25
+   :header-rows: 1
+
+   * - Build argument
+     - Description
+     - Required
+   * - ``PYTHON_VERSION``
+     -
+     - Yes
+   * - ``PIP_VERSION``
+     -
+     - Yes
+   * - ``SETUPTOOLS_VERSION``
+     -
+     - Yes
+   * - ``UBUNTU_VERSION``
+     -
+     - Defaults to ``22.04``
+
+.. code-block:: bash
+
+  $ cd src/docker/base/
+  $ docker build \
+    --build-arg PYTHON_VERSION=3.11.0 \
+    --build-arg PIP_VERSION=23.0.1 \
+    --build-arg SETUPTOOLS_VERSION=69.0.2 \
+    --build-arg UBUNTU_VERSION=22.04 \
+    -t local:my-base-image .
+
+Building the server image
+-------------------------
+
+.. list-table::
+   :widths: 25 50 25
+   :header-rows: 1
+
+   * - Build argument
+     - Description
+     - Required
+   * - ``BASE_REPOSITORY``
+     -
+     - Defaults to ``flwr/server``
+   * - ``BASE_IMAGE_VERSION``
+     -
+     - Defaults to ``py3.11-ubuntu22.04``
+   * - ``FLWR_VERSION``
+     -
+     - Yes
+
+.. code-block:: bash
+
+  $ cd src/docker/server/
+  $ docker build \
+    --build-arg BASE_IMAGE_VERSION=py3.11-ubuntu22.04 \
+    --build-arg FLWR_VERSION=1.6.0 \
+    -t local:my-server-image .
+
+  $ docker run --rm local:my-server-image --help
+
+note:
+- if you want to use a different your own base image, you will need to set he `BASE_REPOSITORY`.
+
+.. code-block:: bash
+
+  $ cd src/docker/server/
+  $ docker build \
+    --build-arg BASE_REPOSITORY=local \
+    --build-arg BASE_IMAGE_VERSION=my-base-image \
+    --build-arg FLWR_VERSION=1.6.0 \
+    -t local:my-server-image .
+
+  $ docker run --rm local:my-server-image --help

doc/source/index.rst

@@ -160,6 +160,7 @@ The Flower community welcomes contributions. The following docs are intended to
    contributor-how-to-write-documentation
    contributor-how-to-release-flower
    contributor-how-to-contribute-translations
+   contributor-how-to-build-docker-images
 
 .. toctree::
    :maxdepth: 1

src/docker/server/Dockerfile

@@ -1,7 +1,8 @@
 # Copyright 2023 Flower Labs GmbH. All Rights Reserved.
 
 ARG BASE_IMAGE_VERSION=py3.11-ubuntu22.04
-FROM flwr/base:$BASE_IMAGE_VERSION as server
+ARG BASE_REPOSITORY=flwr/base
+FROM $BASE_REPOSITORY:$BASE_IMAGE_VERSION as server
 
 WORKDIR /app
 ARG FLWR_VERSION