5.2. Source-to-image build

Source build enables you to set environment values, one per line, inside your application, by specifying them in a .s2i/environment file in the source repository. The environment variables specified in this file are present during the build process and in the output image.

If you provide a .s2i/environment file in your source repository, source-to-image (S2I) reads this file during the build. This allows customization of the build behavior as the assemble script may use these variables.

In addition to builds, the specified environment variables are also available in the running application itself. For example, to cause the Rails application to start in development mode instead of production:

The complete list of supported environment variables is available in the using images section for each image.

You can add environment variables to the sourceStrategy definition of the build configuration. The environment variables defined there are visible during the assemble script execution and will be defined in the output image, making them also available to the run script and application code.

The build process consists of the following three fundamental elements, which are combined into a final container image:

S2I generates a Dockerfile with the builder image as the first FROM instruction. The Dockerfile generated by S2I is then passed to Buildah.

You can write source-to-image (S2I) scripts in any programming language, as long as the scripts are executable inside the builder image. S2I supports multiple options providing assemble/run/save-artifacts scripts. All of these locations are checked on each build in the following order:

Both the io.openshift.s2i.scripts-url label specified in the image and the script specified in a build configuration can take one of the following forms:

Example S2I scripts

The following example S2I scripts are written in Bash. Each example assumes its tar contents are unpacked into the /tmp/s2i directory.

restore build artifacts
move the application source
build application artifacts
install the artifacts

#!/bin/bash

# restore build artifacts
if [ "$(ls /tmp/s2i/artifacts/ 2>/dev/null)" ]; then
    mv /tmp/s2i/artifacts/* $HOME/.
fi

# move the application source
mv /tmp/s2i/src $HOME/src

# build application artifacts
pushd ${HOME}
make all

# install the artifacts
make install
popd

run the application

#!/bin/bash

# run the application
/opt/application/run.sh

#!/bin/bash

pushd ${HOME}
if [ -d deps ]; then
    # all deps contents to tar stream
    tar cf - deps
fi
popd

#!/bin/bash

pushd ${HOME}
if [ -d deps ]; then
    # all deps contents to tar stream
    tar cf - deps
fi
popd

inform the user how to use the image

#!/bin/bash

# inform the user how to use the image
cat <<EOF
This is a S2I sample builder image, to use it, install
https://github.com/openshift/source-to-image
EOF