One-way bottles in germany will be thrown in the garbage after usage. Some
Docker containers will
be removed or destroyed after execution. But especially for some dependency management tools or task runners it can
be nice to have a persistent directory. We can achieve that with the parameter --volumes-from and a
busybox.
I will show the usage on a Docker container of Composer and
Gradle, but the principle is easy to transfer for other
building or management Docker containers.
For example the composer/composer image has a recommended command like the following.
docker run --rm -v $(pwd):/app composer/composer install
The command from above will download your PHP dependencies that are defined in your
composer.json and
will store them in the vendor directory. Composer has to download the dependencies again if we remove
the vendor directory or changing to an other project with similar dependencies. But the normal behavior
of Composer would be to use the ~/.composer/cache/ directory instead of downloading
again the same dependencies.
We can create a Composer busybox that has just the task to store that cache directory.
docker create -v /composer --name composer_cache busybox
This container can be inserted into the command from above with the --volumes-from parameter.
docker run --rm --volumes-from composer_cache -v $(pwd):/app composer/composer install
Composer does not have to download the dependencies again if we execute the command more than ones, regardless of
whether the vendor directory exists in the project directory or not.
The described problem is even more challenging with my own
Gradle Docker image.
Gradle is storing the dependencies not in the project directory. Means every execution of my Gradle container is
downloading the dependencies and throwing them away after tearing down the container, there is not even something
like a vendor directory in the project directory as something like a first layer cache for
dependencies. For example this check command is downloading
the JUnit pom with every execution.
docker run --rm -v "$PWD":/usr/src/project -w /usr/src/project gradle gradle checkWe can create a Gradle busybox that has just the task to store the downloaded dependencies.
docker create -v /root --name gradle_cache busybox
This container can be inserted into the evil command from above with the parameter --volumes-from to
prevent that downloaded dependencies are thrown away after tearing down the Gradle container.
docker run --rm --volumes-from gradle_cache -v "$PWD":/usr/src/project -w /usr/src/project gradle gradle check