How to share gradle cache with docker containers

Question

We run gradle builds within docker containers (the reason for that is the build requires software we don't want to install on the host; node, wine etc. Not even java or gradle is installed on the host).

Launching each container with an empty cache is annoying slow.

I've set up gradle-4.0's http build cache. That avoided the need to java-compile in most cases. The performance gain is though quite low, because build-time is dominated by downloading dependencies. gradlew --parallel helped to mitigate that a bit, but to really boost the build, downloading should be avoided altogether.

Sharing ~/.gradle as a docker volume is problematic, because it will cause contention when containers run in parallel (https://github.com/gradle/gradle/issues/851).

So, what else can be done to avoid downloading the same artifacts over and over again?

Answer 1

While it is problematic to share gradle caches from containers running in parallel, it is absolutely OK to reuse gradle caches when containers run sequentially. Builds that are launched by jenkins run sequentially.

Jenkins builds can be sped up by using a docker volume for the .gradle folder. The only drawback is, that each job requires its own volume.