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Usage of the GitLab Steps with .gitlab-ci.yml

This document describes how GitLab Steps are integrated into the .gitlab-ci.yml.

GitLab Steps will be integrated using a three-stage execution cycle and replace before_script:, script: and after_script:.

  • setup:: Execution stage responsible for provisioning the environment, including cloning the repository, restoring artifacts, or installing all dependencies. This stage will replace implicitly cloning, restoring artifacts, and cache download.
  • run:: Execution stage responsible for running a test, build, or any other main command required by that job.
  • teardown:: Execution stage responsible for cleaning the environment, uploading artifacts, or storing cache. This stage will replace implicit artifacts and cache uploads.

Before we can achieve three-stage execution we will ship minimal initial support that does not require any prior GitLab integration.

Phase 1: Initial support

Initially the Step Runner will be used externally, without any prior dependencies to GitLab:

  • The step-runner will be provided as part of a container image.
  • The step-runner will be explicitly run in the script: section.
  • The $STEPS environment variable will be executed as type: steps. 
hello-world:
  image: registry.gitlab.com/gitlab-org/step-runner
  variables:
    STEPS: |
      - step: gitlab.com/josephburnett/component-hello-steppy@master
        inputs:
          greeting: "hello world"
  script:
    - /step-runner ci

Phase 2: The addition of run: to .gitlab-ci.yml

In Phase 2 we will add run: as a first class way to use GitLab Steps:

  • run: will use a type: steps syntax.
  • run: will replace usage of before_script, script and after_script.
  • All existing functions to support Git cloning, artifacts, and cache would continue to be supported.
  • It is yet to be defined how we would support after_script, which is executed unconditionally or when the job is canceled.
  • run: will not be allowed to be combined with before_script:, script: or after_script:.
  • GitLab Rails would not parse run:, instead it would only perform static validation with a JSON schema provided by the Step Runner. 
hello-world:
  image: registry.gitlab.com/gitlab-org/step-runner
  run:
    - step: gitlab.com/josephburnett/component-hello-steppy@master
      inputs:
        greeting: "hello world"

The following example would fail syntax validation: 

hello-world:
  image: registry.gitlab.com/gitlab-org/step-runner
  run:
    - step: gitlab.com/josephburnett/component-hello-steppy@master
      inputs:
        greeting: "hello world"
  script: echo "This is ambiguous and invalid example"

Transitioning from before_script:, script: and after_script:

GitLab Rails would automatically convert the *script: syntax into relevant run: specification:

  • Today before_script: and script: are joined together as a single script for execution.
  • The after_script: section is always executed in a separate context, representing a separate step to be executed.
  • It is yet to be defined how we would retain the existing behavior of after_script, which is always executed regardless of the job status or timeout, and uses a separate timeout.
  • We would retain all implicit behavior which defines all environment variables when translating script: into step-based execution.

For example, this CI/CD configuration: 

hello-world:
  before_script:
    - echo "Run before_script"
  script:
    - echo "Run script"
  after_script:
    - echo "Run after_script"

Could be translated into this equivalent specification: 

hello-world:
  run:
    - step: gitlab.com/gitlab-org/components/steps/legacy/script@v1.0
      inputs:
        script:
          - echo "Run before_script"
          - echo "Run script"
    - step: gitlab.com/gitlab-org/components/steps/legacy/script@v1.0
      inputs:
        script:
          - echo "Run after_script"
      when: always

Phase 3: The addition of setup: and teardown: to .gitlab-ci.yml

The addition of setup: and teardown: will replace the implicit functions provided by GitLab Runner: Git clone, artifacts and cache handling:

  • The usage of setup: would stop GitLab Runner from implicitly cloning the repository.
  • artifacts: and cache:, when specified, would be translated and appended to setup: and teardown: to provide backward compatibility for the old syntax.
  • release:, when specified, would be translated and appended to teardown: to provide backward compatibility for the old syntax.
  • setup: and teardown: could be used in default: to simplify support of common workflows like where the repository is cloned, or how the artifacts are handled.
  • The split into 3-stage execution additionally improves composability of steps with extends:.
  • The hooks:pre_get_sources_script would be implemented similar to script: and be prepended to setup:.

For example, this CI/CD configuration: 

rspec:
  script:
    - echo "This job uses a cache."
  artifacts:
    paths: [binaries/, .config]
  cache:
    key: binaries-cache
    paths: [binaries/*.apk, .config]

Could be translated into this equivalent specification executed by a step runner: 

rspec:
  setup:
    - step: gitlab.com/gitlab-org/components/git/clone@v1.0
    - step: gitlab.com/gitlab-org/components/artifacts/download@v1.0
    - step: gitlab.com/gitlab-org/components/cache/restore@v1.0
      inputs:
        key: binaries-cache
  run:
    - step: gitlab.com/gitlab-org/components/steps/legacy/script@v1.0
      inputs:
        script:
          - echo "This job uses a cache."
  teardown:
    - step: gitlab.com/gitlab-org/components/artifacts/upload@v1.0
      inputs:
        paths: [binaries/, .config]
    - step: gitlab.com/gitlab-org/components/cache/restore@v1.0
      inputs:
        key: binaries-cache
        paths: [binaries/*.apk, .config]

Inheriting common operations with default:

setup: and teardown: are likely to become very verbose over time. One way to simplify them is to allow inheriting the common setup: and teardown: operations with default:.

The previous example could be simplified to: 

default:
  setup:
    - step: gitlab.com/gitlab-org/components/git/clone@v1.0
    - step: gitlab.com/gitlab-org/components/artifacts/download@v1.0
    - step: gitlab.com/gitlab-org/components/cache/restore@v1.0
      inputs:
        key: binaries-cache
  teardown:
    - step: gitlab.com/gitlab-org/components/artifacts/upload@v1.0
      inputs:
        paths: [binaries/, .config]
    - step: gitlab.com/gitlab-org/components/cache/restore@v1.0
      inputs:
        key: binaries-cache
        paths: [binaries/*.apk, .config]

rspec:
  run:
    - step: gitlab.com/gitlab-org/components/steps/legacy/script@v1.0
      inputs:
        script:
          - echo "This job uses a cache."

linter:
  run:
    - step: gitlab.com/gitlab-org/components/steps/legacy/script@v1.0
      inputs:
        script:
          - echo "Run linting"

Parallel jobs and setup:

With the introduction of setup: at some point in the future we will introduce an efficient way to parallelize the jobs:

  • setup: would define all steps required to provision the environment.
  • The result of setup: would be snapshot and distributed as the base for all parallel jobs, if parallel: N is used.
  • The run: and teardown: would be run on top of cloned job, and all its services.
  • The runner would control and intelligently distribute all parallel jobs, significantly cutting the resource requirements for fixed parts of the job (Git clone, artifacts, installing dependencies.) 
rspec-parallel:
  image: ruby:3.2
  services: [postgres, redis]
  parallel: 10
  setup:
    - step: gitlab.com/gitlab-org/components/git/clone@v1.0
    - step: gitlab.com/gitlab-org/components/artifacts/download@v1.0
      inputs:
        jobs: [setup-all]
    - script: bundle install --without production
  run:
    - script: bundle exec knapsack

Potential GitLab Runner flow:

  1. Runner receives the rspec-parallel job with setup: and parallel: configured.
  2. Runner executes a job on top of Kubernetes cluster using block volumes up to the setup.
  3. Runner then runs 10 parallel jobs in Kubernetes, overlaying the block volume from 2 and continue execution of run: and teardown:.