source-to-image (sti)

Source-to-image (sti) is a tool for building reproducible Docker images. sti produces ready-to-run images by injecting source code into a Docker image and assembling a new Docker image which incorporates the builder image and built source. The result is then ready to use with docker run. sti supports incremental builds which re-use previously downloaded dependencies, previously built artifacts, etc.

Interested in learning more? Read on!

Want to just get started now? Check out the instructions.

Philosophy

1. Simplify the process of application source + builder image -> usable image for most use cases (the 80%)
2. Define and implement a workflow for incremental builds that eventually uses only Docker primitives
3. Develop tooling that can assist in verifying that two different builder images result in the same docker run outcome for the same input
4. Use native Docker primitives to accomplish this - map out useful improvements to Docker that benefit all image builders

Anatomy of a builder image

Creating builder images is easy. sti looks for you to supply the following scripts to use with an image:

1. assemble - builds and/or deploys the source
2. run- runs the assembled artifacts
3. save-artifacts (optional) - captures the artifacts from a previous build into the next incremental build
4. usage (optional) - displays builder image usage information

Additionally for the best user experience and optimized sti operation we suggest images to have /bin/sh and tar commands available.

Users can also set extra environment variables in the application source code. They are passed to the build, and the assemble script consumes them. All environment variables are also present in the output application image. These variables are defined in the .sti/environment file inside the application sources. The format of this file is a simple key-value, for example:

FOO=bar

In this case, the value of FOO environment variable will be set to bar.

See here for a detailed description of the requirements and scripts along with examples of builder images.

Build workflow

The sti build workflow is:

1. sti creates a container based on the build image and passes it a tar file that contains:
   1. The application source in src
   2. The build artifacts in artifacts (if applicable - see incremental builds)
2. sti sets the environment variables from .sti/environment (optional)
3. sti starts the container and runs its assemble script
4. sti waits for the container to finish
5. sti commits the container, setting the CMD for the output image to be the run script and tagging the image with the name provided.

Using ONBUILD images

In case you want to use one of the official Docker language stack images for your build you don't have do anything extra. STI is capable of recognizing the Docker image with ONBUILD instructions and choosing the OnBuild strategy. This strategy will trigger all ONBUILD instructions and execute the assemble script (if it exists) as the last instruction.

Since the ONBUILD images usually don't provide any entrypoint, in order to use this build strategy you will have to provide one. You can either include the 'run', 'start' or 'execute' script in your application source root folder or you can specify a valid STI script URL and the 'run' script will be fetched and set as an entrypoint in that case.

Incremental builds

sti automatically detects:

• Whether a builder image is compatible with incremental building
• Whether a previous image exists, with the same name as the output name for this build

If a save-artifacts script exists, a prior image already exists, and the --incremental=true option is used, the workflow is as follows:

1. sti creates a new Docker container from the prior build image
2. sti runs save-artifacts in this container - this script is responsible for streaming out a tar of the artifacts to stdout
3. sti builds the new output image:
   1. The artifacts from the previous build will be in the artifacts directory of the tar passed to the build
   2. The build image's assemble script is responsible for detecting and using the build artifacts

NOTE: The save-artifacts script is responsible for streaming out dependencies in a tar file.

Dependencies

1. Docker >= 1.6
2. Go >= 1.4

Installation

Assuming Go and Docker are installed and configured, execute the following commands:

$ go get github.com/openshift/source-to-image
$ cd ${GOPATH}/src/github.com/openshift/source-to-image
$ export PATH=$PATH:${GOPATH}/src/github.com/openshift/source-to-image/_output/local/go/bin/
$ hack/build-go.sh

Security

Since the sti command uses the Docker client library, it has to run in the same security context as the docker command. For some systems, it is enough to add yourself into the 'docker' group to be able to work with Docker as 'non-root'. In the latest versions of Fedora/RHEL, it is recommended to use the sudo command as this way is more auditable and secure.

If you are using the sudo docker command already, then you will have to also use sudo sti to give STI permission to work with Docker directly.

Getting Started

You can start using sti right away (see releases) with the following test sources and publicly available images:

$ sti build git://github.com/pmorie/simple-ruby openshift/ruby-20-centos7 test-ruby-app
$ docker run --rm -i -p :9292 -t test-ruby-app

$ sti build git://github.com/bparees/openshift-jee-sample openshift/wildfly-8-centos test-jee-app
$ docker run --rm -i -p :8080 -t test-jee-app

Interested in more advanced sti usage? See here for detailed descriptions of the different CLI commands with examples.