GitLab CI

Description

Create and review .gitlab-ci.yml files. Based on GitLab CI official best practices, DRY/SSOT design patterns, and company standards.

Applicable scenarios:

• Creating .gitlab-ci.yml for new projects
• Reviewing existing .gitlab-ci.yml
• Optimizing CI/CD pipeline performance and maintainability

Creation mode: Confirm project tech stack and deployment approach → generate configuration based on rules below → self-check against all rules.

Review mode: Read .gitlab-ci.yml and files referenced by include: → check against rules item by item (annotate ID) → output report:

• Must Fix: Violates mandatory rules
• Suggested Improvement: Does not follow best practices
• Optional Optimization: Further optimization opportunity

Company Standards

Runner Tag Convention

Tag	Purpose
sonar-scanner	General CI tasks

Set uniformly via default.tags:

default:
  tags:
    - sonar-scanner

Docker Image Convention

Manage image versions uniformly via top-level variables:; hard-coding in jobs is prohibited:

variables:
  PYTHON_IMAGE: python:3.11-slim
  NODE_IMAGE: node:20-slim
  GO_IMAGE: golang:1.22-alpine

ArgoCD GitOps Integration

CI is only responsible for Build & Test & Publish; deployment is triggered via ArgoCD GitOps:

• CI builds image → pushes to Registry → updates image tag in GitOps repo
• ArgoCD watches GitOps repo changes → auto-syncs to cluster
• Preview environments: MR branches auto-create temporary namespaces, destroyed after merge

Red line: Directly running kubectl apply / helm install to production environments from CI is prohibited.

Rules

DRY (Don't Repeat Yourself)

D1: default: for shared configuration

tags, image, interruptible, retry, and other cross-job shared configuration must go in default:; repeating in each job is prohibited.

D2: extends: to eliminate job duplication

When multiple jobs share the same configuration, extract a hidden job (.job-name) as a base class; child jobs inherit via extends:.

D3: YAML anchors to reuse data blocks

Use YAML anchors (&anchor / *anchor) for duplicated pure data (such as rules: condition lists).

D4: !reference for selective reuse

When only a specific property of a job needs reuse (not the entire job), use !reference [.job, attribute].

SSOT (Single Source of Truth)

S1: include: to reference shared templates

Company-level CI templates must be referenced from your-org/ci-templates via include:project:; copy-pasting is prohibited:

include:
  - project: your-org/ci-templates
    ref: main
    file:
      - /.gitlab-ci/jobs/mr-doc-check.yml

S2: variables: for centralized mutable values

Image versions, service names, regions, and other mutable values must be defined as top-level variables:; hard-coding in script: is prohibited.

S3: workflow:rules: for unified pipeline trigger strategy

Use workflow:rules: at the top of the file to define when to create pipelines, avoiding each job defining redundant trigger conditions separately.

Structure and Modern Syntax

ID	Rule	Severity
R1	Use rules: instead of only:/except: (deprecated)	Must Fix
R2	Use needs: to build DAG and reduce pipeline time	Suggested
R3	Define workflow:rules: to avoid duplicate pipelines	Suggested
R4	stages: order is logical (lint → build → test → publish → deploy)	Suggested

Reliability

ID	Rule	Severity
R5	All jobs set reasonable timeout:	Suggested
R6	Network-dependent jobs configure retry: + when: conditions	Suggested
R7	Non-deployment jobs set interruptible: true	Suggested
R8	Jobs requiring resource cleanup use after_script:	Optional

Security

ID	Rule	Severity
R9	No hard-coded secrets/credentials in yml	Must Fix
R10	Sensitive variables use CI/CD Variables (masked + protected)	Must Fix
R11	Production deployment jobs restricted to protected branches/tags	Must Fix

Performance

ID	Rule	Severity
R12	artifacts: set expire_in: to prevent storage bloat	Suggested
R13	cache: configured with correct key: and policy:	Suggested
R14	Large test suites use parallel: for sharding	Optional
R15	Deployment jobs use resource_group: to prevent concurrent conflicts	Suggested

Examples

Bad

1. Violating DRY — Extensive configuration duplication

build-frontend:
  stage: build
  image: node:20-slim
  tags:
    - sonar-scanner
  script:
    - npm ci
    - npm run build
  rules:
    - if: '$CI_PIPELINE_SOURCE == "merge_request_event"'

build-backend:
  stage: build
  image: golang:1.22-alpine
  tags:
    - sonar-scanner
  script:
    - go build ./...
  rules:
    - if: '$CI_PIPELINE_SOURCE == "merge_request_event"'

test-frontend:
  stage: test
  image: node:20-slim
  tags:
    - sonar-scanner
  script:
    - npm test
  rules:
    - if: '$CI_PIPELINE_SOURCE == "merge_request_event"'

Issues: tags repeated 3 times (violates D1), rules repeated 3 times (violates D3), images hard-coded (violates S2).

2. Deprecated syntax + direct deployment

deploy:
  stage: deploy
  only:
    - main
  script:
    - kubectl apply -f k8s/ --kubeconfig /tmp/kubeconfig
  variables:
    IMAGE: registry.example.com/my-service:latest

Issues: Uses only: deprecated syntax (R1), directly runs kubectl apply to the cluster (ArgoCD red line), latest tag is not traceable (S2).

3. Copy-paste templates

# Copied lint configuration from another project
lint:
  stage: lint
  image: golangci/golangci-lint:v1.55
  script:
    - golangci-lint run
  tags:
    - sonar-scanner
  rules:
    - if: '$CI_PIPELINE_SOURCE == "merge_request_event"'
  allow_failure: true
  # 30 lines of identical configuration repeated across 5 projects...

Issues: Should be extracted to your-org/ci-templates (violates S1); cross-project maintenance cost is high, changes require 5 modifications.

Good

1. DRY + SSOT Standard Approach

variables:
  NODE_IMAGE: node:20-slim
  GO_IMAGE: golang:1.22-alpine

default:
  tags:
    - sonar-scanner
  interruptible: true
  retry:
    max: 2
    when:
      - runner_system_failure

workflow:
  rules:
    - if: '$CI_PIPELINE_SOURCE == "merge_request_event"'
    - if: '$CI_COMMIT_BRANCH == "main"'

.mr-only:
  rules: &mr-rules
    - if: '$CI_PIPELINE_SOURCE == "merge_request_event"'

include:
  - project: your-org/ci-templates
    ref: main
    file:
      - /.gitlab-ci/jobs/mr-doc-check.yml

stages:
  - build
  - test
  - publish

build-frontend:
  stage: build
  image: $NODE_IMAGE
  rules: *mr-rules
  script:
    - npm ci
    - npm run build
  artifacts:
    paths: [dist/]
    expire_in: 1 day

build-backend:
  stage: build
  image: $GO_IMAGE
  rules: *mr-rules
  script:
    - go build ./...

test-frontend:
  stage: test
  image: $NODE_IMAGE
  rules: *mr-rules
  needs: [build-frontend]
  script:
    - npm test
  coverage: '/coverage: \d+\.\d+%/'

Strengths:

• default: unifies tags/retry/interruptible (D1)
• YAML anchor &mr-rules reuses trigger conditions (D3)
• variables: manages image versions (S2)
• include: references company templates (S1)
• workflow:rules: unifies trigger strategy (S3)
• needs: accelerates DAG (R2)
• artifacts:expire_in: controls storage (R12)

2. ArgoCD GitOps Integration

publish:
  stage: publish
  image: docker:24
  services:
    - docker:24-dind
  script:
    - docker build -t $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA .
    - docker push $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA
  rules:
    - if: '$CI_COMMIT_BRANCH == "main"'

gitops-update:
  stage: deploy
  image: alpine/git:latest
  script:
    - git clone https://gitlab-ci-token:${GITOPS_TOKEN}@gitlab.example.com/your-org/gitops.git
    - cd gitops/apps/my-service
    - "sed -i 's|image:.*|image: ${CI_REGISTRY_IMAGE}:${CI_COMMIT_SHA}|' values.yaml"
    - git commit -am "chore: update my-service to ${CI_COMMIT_SHA}"
    - git push
  rules:
    - if: '$CI_COMMIT_BRANCH == "main"'
  resource_group: production

Strengths: CI only builds and pushes images; deployment is triggered by updating the GitOps repo for ArgoCD (separation of concerns). $CI_COMMIT_SHA ensures image traceability. resource_group: prevents concurrent deployments (R15).

Exemptions

Scenario	Condition
Minimal project	Only lint/test with no deployment needs — ArgoCD integration may be omitted
Legacy project migration	only:/except: may be temporarily retained during migration; a migration plan is required
One-off scripts	Temporary CI jobs may be simplified; must annotate # TODO: cleanup

References

• GitLab CI/CD YAML syntax reference
• GitLab CI/CD pipeline efficiency
• GitLab CI/CD rules: keyword
• GitLab CI/CD needs: keyword
• GitLab CI/CD include: keyword