OSBuild Composer

Operating System Image Composition Services

The composer project is a set of HTTP services for composing operating system images. It builds on the pipeline execution engine of osbuild and defines its own class of images that it supports building.

Multiple APIs are available to access a composer service. This includes support for the lorax-composer API, and as such can serve as drop-in replacement for lorax-composer.

You can control a composer instance either directly via the provided APIs, or through higher-level user-interfaces from external projects. This, for instance, includes a Cockpit Module or using the composer-cli command-line tool.



Composer is a middleman between the workhorses from osbuild and the user-interfaces like cockpit-composer, composer-cli, or others. It defines a set of high-level image compositions that it supports building. Builds of these compositions can be requested via the different APIs of Composer, which will then translate the requests into pipeline-descriptions for osbuild. The pipeline output is then either provided back to the user, or uploaded to a user specified target.

The following image visualizes the overall architecture of the OSBuild infrastructure and the place that Composer takes:


Consult the osbuild-composer(7) man-page for an introduction into composer, information on running your own composer instance, as well as details on the provided infrastructure and services.


The requirements for this project are:

  • osbuild >= 11
  • systemd >= 244

At build-time, the following software is required:

  • go >= 1.13
  • python-docutils >= 0.13


The standard go package system is used. Consult upstream documentation for detailed help. In most situations the following commands are sufficient to build and install from source:

mkdir build
go build -o build ./...

The man-pages require python-docutils and can be built via:

make man


Pull request gating

Each pull request against osbuild-composer starts a series of automated tests. Tests run via GitHub Actions and Jenkins. Each push to the pull request will launch theses tests automatically.

Jenkins only tests pull requests from members of the osbuild organization in GitHub. A member of the osbuild organization must say ok to test in a pull request comment to approve testing. Anyone can ask for testing to run by saying the bot's favorite word, schutzbot, in a pull request comment. Testing will begin shortly after the comment is posted.

Test results in Jenkins are available by clicking the Details link on the right side of the Schutzbot check in the pull request page.


  • Apache-2.0
  • See LICENSE file for details.