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Simple python library for building docker images.
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atomic_reactor release Jan 23, 2020
docs koji docs: describe source containers koji metadata Dec 10, 2019
images Switch to using libmodulemd v2 API for Python Jul 25, 2019
rel-eng Fix rel-eng/packages/atomic-reactor May 5, 2017
tests Whitelist annotation must be set as string Jan 23, 2020
.flake8 Add .flake8 file so that Stickler CI would know about agreed settings May 5, 2017
.landscape.yml Add a .landscape.yml to add checks in Python 3 mode May 22, 2016
.stickler.yml Enable shellcheck (bash) lint Dec 2, 2019
.travis.yml Use podman as testing container engine Dec 2, 2019 Revert "Remove section about docker-py" Nov 11, 2019
Dockerfile Add plugins for Flatpak creation Sep 14, 2017
LICENSE Remove the remaining mentions of dock Oct 29, 2015 Revert "Make requirements.txt work for Fedora and RHEL/CentOS 7" Apr 10, 2019 change organization references from projectatomic to containerbuildsy… Jun 4, 2019
atomic-reactor.spec spec: update hash for Jan 23, 2020
requirements-py2.txt Revert "Make requirements.txt work for Fedora and RHEL/CentOS 7" Apr 10, 2019
requirements.txt Revert "Change docker-py requirement to docker" Nov 11, 2019 release Jan 23, 2020 Use podman as testing container engine Dec 2, 2019

Atomic Reactor

Build Status Code Health Coverage Status Code Quality: Python Total Alerts

Python library with command line interface for building docker images.


  • push image to registry when it's built
  • build inside a docker container (so your builds are separated between each other)
  • git as a source to your Dockerfile (you may specify commit/branch and path to Dockerfile within the git repo)
  • collect build logs
  • integration with koji build system
  • integration with fedora packaging system
  • inject arbitrary yum repo inside Dockerfile (change source of your packages)
  • retag base image so it matches FROM instruction in Dockerfile
  • change base image (FROM) in your Dockerfile
  • run simple tests after your image is built

There are several build modes available:

  • building within a docker container using docker from host by mounting docker.sock inside the container
  • building within a privileged docker container (new instance of docker is running inside)
  • executing build within current environment


for Fedora users

$ sudo dnf install atomic-reactor python-atomic-reactor-koji

from git

Clone this git repo and install Atomic Reactor using python installer:

$ git clone
$ cd atomic-reactor
$ sudo pip install .

You don't even need to install it. You may use it straight from git:

$ alias atomic-reactor="python ${REACTOR_PATH}/atomic-reactor/cli/"


  • docker-py.
  • koji plugin requires koji package, which is not available on PyPI: you have to install it manually:
$ sudo dnf install koji


If you would like to build your images within build containers, you need to obtain images for those containers. We call them build images. Atomic Reactor is installed inside and used to take care of build itself.

You can either get the build image from Dockerhub or create it yourself.

getting build image from Dockerhub

Just use

$ docker pull slavek/atomic-reactor

This will pull the buildroot image with the latest Atomic Reactor commits. Images with stable releases are available since version 1.3.3 and you can access them by using the version specifier as a tag, such as

$ docker pull slavek/atomic-reactor:1.3.3

installation from git

$ atomic-reactor create-build-image --reactor-local-path ${PATH_TO_REACTOR_GIT} ${PATH_TO_REACTOR_GIT}/images/dockerhost-builder buildroot

Why is it so long? Okay, let's get through. First thing is that Atomic Reactor needs to install itself inside the build image. You can pick several sources for Atomic Reactor: your local copy, (this) official upstream repo, your forked repo or even distribution tarball. In the example above, we are using our locally cloned git repo (--reactor-local-path ${PATH_TO_REACTOR_GIT}).

You have to provide Dockerfile too. Luckily these are part of upstream repo (see folder images). It's the first argument: ${PATH_TO_REACTOR_GIT}/images/dockerhost-builder.

And finally, you need to name the image: buildroot.

installation from RPM

$ atomic-reactor create-build-image --reactor-tarball-path /usr/share/atomic-reactor/atomic-reactor.tar.gz /usr/share/atomic-reactor/images/dockerhost-builder buildroot-fedora

Section above contains detailed description. Let's make this short.

  1. --reactor-tarball-path — Atomic Reactor needs to install itself into build image: this is how you specify where Atomic Reactor gets its own sources (when installed via RPM, Atomic Reactor provides itself packaged as tarball at /usr/share/atomic-reactor/atomic-reactor.tar.gz)
  2. first argument is path do dockerfile — dockerfiles for both methods are available at /usr/share/atomic-reactor/images/, just pick one
  3. and finally, second argument names the build image

getting Atomic Reactor from distribution

Or you can build the image using docker and install Atomic Reactor directly from distribution:

FROM fedora:latest
RUN dnf -y install docker-io git python-docker-py python-setuptools koji atomic-reactor && dnf clean all
CMD ["atomic-reactor", "-v", "inside-build", "--input", "path"]

and command:

$ docker build -t buildroot-hostdocker .

And now you can build your images!

As soon as our build image is built, we can start building stuff in it:

$ atomic-reactor build git --method hostdocker --build-image buildroot-hostdocker --image test-image --uri ""

The built image will be in the build container. Therefore, this example doesn't make much sense. If you would like to access the built image, you should probably push it to your registry and build it like this:

$ atomic-reactor build git --method hostdocker \
             --build-image buildroot-hostdocker \
             --image test-image \
             --target-registries \
             --uri ""

Both of these examples use the git source provider (atomic-reactor build git), which gets the source code to put in the image from a git repo. There are also other providers:

  • path - uses source code from local path
  • json - accepts a path to build json file with all info needed for build

IP address should be address of docker0 network interface. Update it if yours is different. Also, don't forget to start the registry.

Bear in mind that you shouldn't mix build methods. If you use hostdocker method with build image for privileged method, then it won't work.

Further reading

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