how to prevent gitlab ci from downloading sbt every time?

Question

We have a play2/scala application which we are building with gitlab ci.

Our .gitlab-ci.yml (at least the important part) looks as follows:

Answer 1

If you don't want to use custom made images, the best solution is to use Gitlab CI's caching mechanism.

It's a little hard to get it right, but this blog post describes how to do it for SBT.

Example .gitlab-ci.yml

Quoted from the blog post, minor errors corrected by myself:

# some parts originally from https://github.com/randm-ch/units-of-information/blob/master/.gitlab-ci.yml

image: "hseeberger/scala-sbt"

variables:
  SBT_VERSION: "0.13.9"
  SBT_OPTS: "-Dsbt.global.base=sbt-cache/.sbtboot -Dsbt.boot.directory=sbt-cache/.boot -Dsbt.ivy.home=sbt-cache/.ivy"

cache:
  key: "$CI_BUILD_REF_NAME" # contains either the branch or the tag, so it's caching per branch
  untracked: true
  paths:
    - "sbt-cache/.ivy/cache"
    - "sbt-cache/.boot"
    - "sbt-cache/.sbtboot"
    - "sbt-cache/target"

stages:
  - test

test:
  script:
    - sbt test

Second example, also including apt-get caching

This is what I used for my project, usable for more general use cases and Docker images:

image: java:8

stages:
  - test

variables:
  SBT_VERSION: "0.13.9"
  SBT_OPTS: "-Dsbt.global.base=sbt-cache/.sbtboot -Dsbt.boot.directory=sbt-cache/.boot -Dsbt.ivy.home=sbt-cache/.ivy"
  SBT_CACHE_DIR: "sbt-cache/.ivy/cache"

cache:
  key: "$CI_BUILD_REF_NAME" # contains either the branch or the tag, so it's caching per branch
  untracked: true
  paths:
    - "apt-cache/"
    - "sbt-cache/.ivy/cache"
    - "sbt-cache/.boot"
    - "sbt-cache/.sbtboot"
    - "sbt-cache/target"

before_script:
  - export APT_CACHE_DIR=`pwd`/apt-cache
  - mkdir -pv $APT_CACHE_DIR
  - ls $APT_CACHE_DIR || echo "no apt-cache dir found"
  - apt-get -o dir::cache::archives=$APT_CACHE_DIR update -y
  - apt-get -o dir::cache::archives=$APT_CACHE_DIR install apt-transport-https -y
  # Install SBT
  - mkdir -pv $SBT_CACHE_DIR
  - ls $SBT_CACHE_DIR || echo "no ivy2 cache fir found"
  - echo "deb http://dl.bintray.com/sbt/debian /" | tee -a /etc/apt/sources.list.d/sbt.list
  - apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv 642AC823
  - apt-get -o dir::cache::archives=$APT_CACHE_DIR update -y
  - apt-get -o dir::cache::archives=$APT_CACHE_DIR install sbt -y
  - sbt -v sbtVersion

test:
  stage: test
  script:
     - sbt -v sbtVersion