Merge pull request #6640 from qlyoung/doc-docker-builds

doc: add docker image build instructions

doc/developer/building-docker.rst

@@ -0,0 +1,101 @@
+Docker
+======
+
+This page covers how to build FRR Docker images.
+
+Images
+""""""
+FRR has Docker build infrastructure to produce Docker images containing
+source-built FRR on the following base platforms:
+
+* Alpine
+* Centos 7
+* Centos 8
+
+The following platform images may also be built, but these simply install a
+binary package from an existing repository and do not perform source builds:
+
+* Debian 10
+
+Some of these are available on `DockerHub
+<https://hub.docker.com/repository/docker/frrouting/frr/tags?page=1>`_.
+
+There is no guarantee on what is and is not available from DockerHub at time of
+writing.
+
+Scripts
+"""""""
+
+Some platforms contain an included build script that may be run from the host.
+This will set appropriate packaging environment variables and clean up
+intermediate build images.
+
+These scripts serve another purpose. They allow building platform packages
+without needing the platform. For example, the Centos 8 docker image can also
+be leveraged to build Centos 8 RPMs that can then be used separately from
+Docker.
+
+If you are only interested in the Docker images and don't want the cleanup
+functionality of the scripts you can ignore them and perform a normal Docker
+build. If you want to build multi-arch docker images this is required as the
+scripts do not support using Buildkit for multi-arch builds.
+
+Building Alpine Image
+---------------------
+
+Script::
+
+   ./docker/alpine/build.sh
+
+No script::
+
+   docker build -f docker/alpine/Dockerfile .
+
+No script, multi-arch (ex. amd64, arm64, armv7)::
+
+   docker buildx build --platform linux/amd64,linux/arm64,linux/arm/v7 -f docker/alpine/Dockerfile -t frr:latest .
+
+
+Building Debian Image
+---------------------
+
+::
+
+   cd docker/debian
+   docker build .
+
+Multi-arch (ex. amd64, arm64, armv7)::
+
+   cd docker/debian
+   docker buildx build --platform linux/amd64,linux/arm64,linux/arm/v7 -t frr-debian:latest .
+
+Building Centos 7 Image
+-----------------------
+
+Script::
+
+   ./docker/centos-7/build.sh
+
+No script::
+
+   docker build -f docker/centos-7/Dockerfile .
+
+No script, multi-arch (ex. amd64, arm64)::
+
+   docker buildx build --platform linux/amd64,linux/arm64 -f docker/centos-7/Dockerfile -t frr-centos7:latest .
+
+
+Building Centos 8 Image
+-----------------------
+
+Script::
+
+   ./docker/centos-8/build.sh
+
+No script::
+
+   docker build -f docker/centos-8/Dockerfile .
+
+No script, multi-arch (ex. amd64, arm64)::
+
+   docker buildx build --platform linux/amd64,linux/arm64 -f docker/centos-8/Dockerfile -t frr-centos8:latest .

doc/developer/building.rst

@@ -28,3 +28,4 @@ Building FRR
    building-frr-for-ubuntu1804
    building-frr-for-ubuntu2004
    building-frr-for-archlinux
+   building-docker