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Cross-project build artifacts dependencies

Problem to Solve

With recently added cool feature of specifying dependencies between stages (gitlab-ce#14211) it's now possible to re-use built artifacts across stages by adding a few lines in .gitlab-ci.yml. What's missing though is an extension to this feature, allowing to easily specify dependency on some build's some stage's artifact from another project.

Currently in the build for executable project I'm simply re-building libraries' code every time I build an executable, which is waste of time and resources. The feature of cross-project dependencies would solve the problem elegantly and make life easier, i.e. no need for additional API keys, curl'ing, secure variables, etc. It also may help others requesting features like gitlab-ce#4768 (better links for artifacts).

Proposal

To implement this behavior, we'll add new keywords for needs which can reference another project/ref/artifacts in incremental steps as follows:

  1. Remove the need for dependencies 
generate_content:
  needs:
    - job: another-job-in-this-pipeline
      artifacts: true

MR that implements this step: !19943 (merged)

  1. Make cross-project job dependency with Bridge
generate_content:
  needs:
    - project: this_project # This is addition to mark this dependency as a Bridge job
      ref: master # This is to filter for the Bridge job 
      job: another-job-in-another-pipeline
      artifacts: true

This will bring in the last successfully built artifacts from the another-job-in-another-pipeline job on the master branch of the project this_project.

Reference

The following is the original proposal in the issue.

Original Example

Suppose I have a library project my-library and some other project my-exe which needs artifacts from my-library's build stage during its build. So, under the proposal, my-exe's .gitlab-ci.yml may look something like this:

...

# build job of my-exe project
build:linux:
  stage: build
  dependencies:
  - project: quyse/my-library # mandatory, name of the project
    commit: 123456789abcdef123456789abcdef123456789a # optional, commit hash in my-library repository
    branch: master # optional, branch name in my-library repository
    tag: v1.1 # optional, tag name in my-library repository
    # could be other filters
    job: linux-x64 # mandatory, job name defined in .gitlab-ci.yml in my-library
  script:
    ...

...

So here CI is supposed to fetch artifacts of the linux-x64 job of the build of my-library project made for specified branch and commit (or specified tag), and unpack them into runner's working directory of my-exe build (in the same way as it does currently).

Notes

  • There's no ambiguity with current usage of dependencies field: string value may still mean dependency on some other stage of the same project, and only if it's a YAML map value, then it's an external (cross-project) dependency.
  • commit, branch and tag fields are all optional, and work as a filter, they may be used simultaneously to resolve ambiguity: for example there could be multiple builds corresponding to the single commit (in different branches), and of course there're multiple builds corresponding to the single branch. (Actually even with both commit and branch/tag specified it could still be multiple builds, for example, if build has been retried, or branch deleted/re-pushed, or whatever). So if there're multiple builds, CI can just use the latest one.
  • Probably CI must always use the latest successful build (from the list of builds matching the filter), i.e. the build where all the stages (not marked with allow_failure) are successful, not just the one we are using artifacts from. (Just not sure if such a concept already exists).
  • If there's no matching builds of the library, the dependent build must wait until one appears (essentially, in the same way as dependent stages are waiting for their dependencies currently).
  • CI runner should fetch artifacts using its API token, so it should be allowed to access private projects it has been added to (or if it's added to the group, or whatever other rules apply here).
  • It looks reasonable that this feature will only work across projects of the single Gitlab server.
Edited by Marius Bobin