source-to-image/docs/builder_image.md

sti builder image requirements

The main advantage of using sti for building reproducible docker image ease of use for developer. To meet that criteria you, as a builder image author, should be aware of the two basic requirements for the best possible sti performance, these are:

• required image contents
• sti scripts

Required image contents

The build process consists of three fundamental elements which are combined into final docker image, the three are: sources, scripts and builder image. During the build process sti must place sources and scripts inside that builder image. To do so sti creates a tar file containing the two and then streams that file into the builder image. Before executing assemble script, sti untars that file and places its contents into the location specified with --location flag or STI_LOCATION environment variable from the builder image (default location is /tmp). For this to happen your image must supply tar archiving utility (command tar available in $PATH) and command line interpreter (command /bin/sh). Doing so will allow your image to use the fastest possible build path, because in all other cases when either tar or /bin/sh is not available, sti build will be forced to perform an additional docker build to put both sources and scripts inside the image and only then run the usual sti build procedure (sti will do this automatically if tar and /bin/sh are not found). See the following diagram for how build workflow looks like:

* Run build's responsibility is to untar the sources, scripts and artifacts (if such exist) and invoke assemble script. If this is second run (after catching tar//bin/sh error) it's responsible only for invoking assemble script, since both scripts and sources are already there.

sti scripts

sti expects you, as the builder image author, to supply the following scripts:

• required:
  • assemble
  • run
• optional:
  • save-artifacts
  • usage

All of the scripts can be written in any programming language, as long as it is executable inside the builder image.

assemble

The assemble script is responsible for building the application artifacts from source, and place them into appropriate directories inside the image. The workflow for assemble is:

1. Restore build artifacts (in case you want to support incremental builds, make sure to define save-artifacts) as well.
2. Place the application source in desired location.
3. Build application artifacts.
4. Install the artifacts into locations appropriate for running.

Example assemble script:

NOTE: All the examples are written in Bash and it is assumed all the tar contents is unpacked into /tmp/sti directory.

#!/bin/bash

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

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

# build application artifacts
pushd ${HOME}
make all

# install the artifacts
make install
popd

run

The run script is responsible for executing your application.

Example run script:

#!/bin/bash

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

save-artifacts

The save-artifacts script is responsible for gathering all the dependencies which existence can speed up the following build processes (eg. for Ruby - Gemfiles, for Java - .m2 contents, etc.) into a tar file and stream it to the standard output.

Example save-artifacts script:

#!/bin/bash

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

usage

The usage script is for you, as the builder image author, to inform the user how to properly use your image.

Example usage script:

#!/bin/bash

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