gitlab 8.2.1, How to use cache in .gitlab-ci.yml

8.2 only supports per-job cache, and 8.3 will introduce "group" cache that serves among jobs according to @ayufan's comment in Possibility to cache folders in build directory (#97).

However, although I cannot be 100% sure, by quick digging the source code of gitlab-ci-muti-runner, docker executor doesn't seems to work with the cache functionality. Since a whole new container is created and destroyed in every job, the cache.tgz archive would no longer exist in the next build.

Errata:

The above description is incorrect due to testing in a misconfigured environment. By default, gitlab-ci-multi-runner creates a dedicated data volume container as a cache storage for each concurrent build. The cache container is mounted to directory /cache in the application container and those cache.tgz tarballs are placed under /cache by default. So caches are actually reusable among independent builds.

Updates 2015/12/11:

Just found out that "group" cache has already been implemented in gitlab-runner@7dc9524f6ef0144b3797fc07c9035f38a8ad0512, maybe not yet released and documented. You can enable it with

cache:
  paths:
    - doc/
  group: sharedcache

The result is one cache tarball being placed under path <namespace>/<repo>/sharedcache/ instead of two cache tarballs being placed separately under path <namespace>/<repo>/createcache/ and <namespace>/<repo>/testcache/.

Updates 2017/12/04:

"group" cache has been replaced by cache:key. Use the key key to make the cache share between jobs or git references. By default, a cache is shared between all jobs. So, simply write the following would do the job

cache:
  paths:
    - doc/

Checkout GitLab CI cache:key and gitlab-runner@d34f76f86a7c2fc4d399e9922175bcc614434016 for more information.

https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/issues/327

image: java:openjdk-8-jdk

before_script:
    - export GRADLE_USER_HOME=`pwd`/.gradle

cache:
  paths:
    - .gradle/wrapper
    - .gradle/caches

build:
  stage: build
  script:
     - ./gradlew assemble

test:
  stage: test
  script:
     - ./gradlew check

It seems it is not possible to cache container local files with shared runners. You have to put your files in e.g. the cache folder:

before_script:
  - export GRADLE_USER_HOME=/cache/.gradle

...

cache:
  paths:
    - $GRADLE_USER_HOME/caches/
    - $GRADLE_USER_HOME/wrapper/
    - $GRADLE_USER_HOME/build-cache/

Strictly it is not required to put the /cache folder as files to cache, because this happens automatically, but I leave it for clarity (also when I want to move the gradle cache)