4.3. Creating images from source code with source-to-image
Source-to-image (S2I) is a framework that makes it easy to write images that take application source code as an input and produce a new image that runs the assembled application as output.
The main advantage of using S2I for building reproducible container images is the ease of use for developers. As a builder image author, you must understand two basic concepts in order for your images to provide the best S2I performance, the build process and S2I scripts.
4.3.1. Understanding the source-to-image build process
The build process consists of the following three fundamental elements, which are combined into a final container image:
- Sources
- Source-to-image (S2I) scripts
- Builder image
S2I generates a Dockerfile with the builder image as the first FROM instruction. The Dockerfile generated by S2I is then passed to Buildah.
4.3.2. How to write source-to-image scripts
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:
- A script specified in the build configuration.
-
A script found in the application source
.s2i/bindirectory. -
A script found at the default image URL with the
io.openshift.s2i.scripts-urllabel.
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:
-
image:///path_to_scripts_dir: absolute path inside the image to a directory where the S2I scripts are located. -
file:///path_to_scripts_dir: relative or absolute path to a directory on the host where the S2I scripts are located. -
http(s)://path_to_scripts_dir: URL to a directory where the S2I scripts are located.
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The suggested location to put the test application built by your |
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.
assemble script:
#!/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 script:
#!/bin/bash # run the application /opt/application/run.sh
save-artifacts script:
#!/bin/bash
pushd ${HOME}
if [ -d deps ]; then
# all deps contents to tar stream
tar cf - deps
fi
popd
usage script:
#!/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
Additional resources
