• Introduction
• Prerequisites
• The GitLab pipeline code
• Integrated features
• Conclusion

Introduction

With GitLab Pages, you can publish static websites directly from a repository in GitLab. By default, we cannot have preview pages: if a job deploys the pages, this overwrites previous content, which disallows preview mode.

Some article on the internet show how to get around that with artifacts, knowing that GitLab can display artifacts. But this trick has disadvantages, mainly highly technical links, that have to be shared again after changes on the branch.

Some Github gist points into the right direction, but in a complex way and with too few side features.

In this article, we will get around the limitation by taking advantage of the cache mechanism, and be able to display per-branch content, with the side benefit of obfuscating the path to ephemeral branches content, if desired.

The solution can be broken down to these steps :

• Generate files for current branch
• Get previous branches generation from GitLab cache
• Merge and update cache
• Auto delete obsolete cache on branch deletion, using GitLab environments

Prerequisites

We assume you already have a way of generating your HTML static content, and just want to serve the files using GitLab Pages.

For the code to work, your cache must be centralized, either by using gitlab.com runners, by having a single runner, or by sharing caches between multiple private runners.

You need to accept a global cache by deactivating the GiLab option Use separate caches for protected branches in Settings -> CICD -> General Pipelines.

The GitLab pipeline code

workflow:
  rules: # disable tag pipelines and duplicate MR pipelines
    - if: $CI_COMMIT_BRANCH

variables:
  EPHEMERAL_BRANCHES_PATH: preview # subpath to ephemeral branches content for preview, anything will work

pages:
  stage: build
  image: alpine:3.18
  cache:
    key: gitlab-pages
    paths: [public]
  before_script:
    # default available 'tree' app in alpine image does not work as intended
    - apk add tree
    # CURRENT_CONTENT_PATH is defined in rules, different between main branch and ephemeral branches
    - mkdir -p public/$CURRENT_CONTENT_PATH && ls public/$CURRENT_CONTENT_PATH/..
    - | # avoid deleting main branch content when cache has been erased
      if [ "$CI_COMMIT_BRANCH" != "$CI_DEFAULT_BRANCH" ] && [ ! -d public/$CI_DEFAULT_BRANCH ]; then
        echo -e "💥\e[91;1m Unable to retrieve $CI_DEFAULT_BRANCH generated files from cache ; please regenerate $CI_DEFAULT_BRANCH files first\e[0m"
        exit 1
      fi
    - rm -rf public/$CURRENT_CONTENT_PATH || true # remove last version of current branch
  script:
    - ./generate-my-html.sh --output build-docs || true # insert here your code that generates documentation
    - mv --verbose build-docs public/$CURRENT_CONTENT_PATH
    - cd public/$EPHEMERAL_BRANCHES_PATH
    - tree -d -H '.' -L 1 --noreport --charset utf-8 -T "Versions" -o index.html # generate a root HTML listing all previews for easier access
  environment:
    name: pages/$CI_COMMIT_BRANCH
    action: start
    url: $CI_PAGES_URL/$CURRENT_CONTENT_PATH
    on_stop: pages-clean-preview
  rules:
    # 'main branch' is exposed at GitLab Pages root
    - if: $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH
      variables:
        CURRENT_CONTENT_PATH: "."
    # other (short-lived) branches generation are exposed in 'EPHEMERAL_BRANCHES_PATH/branch-name-sanitized' sub path
    - variables:
        CURRENT_CONTENT_PATH: $EPHEMERAL_BRANCHES_PATH/$CI_COMMIT_REF_SLUG
  artifacts:
    paths: [public]
    expire_in: 1h

pages-clean-preview:
  stage: build
  image: alpine:3.18
  cache:
    key: gitlab-pages
    paths: [public]
  variables:
    GIT_STRATEGY: none # git files not available after branch deletion
    FOLDER_TO_DELETE: $EPHEMERAL_BRANCHES_PATH/$CI_COMMIT_REF_SLUG # an indirection to allow arbitrary deletion when launching this job
  script:
    - rm -rf public/$FOLDER_TO_DELETE
  environment:
    name: pages/$CI_COMMIT_BRANCH
    action: stop
  rules:
    - if: $CI_COMMIT_BRANCH != $CI_DEFAULT_BRANCH
      when: manual
      allow_failure: true

Integrated features

The above code has below features :

• main content is exposed on $CI_PAGES_URL and the path is configurable with $CURRENT_CONTENT_PATH
• Per-branch preview content is exposed on $CI_PAGES_URL/preview, with a homepage to easily navigate to branches content
• Path to root preview folder is configurable with $EPHEMERAL_BRANCHES_PATH variable to hide preview content by obfuscation
• Generated pages are associated with environments to take advantage of auto-cleaning on branch deletion
• To avoid disturbing already existing environments, pages environment are placed under a pages folder
• If main content has not been generated in current cache, or if the cache has been deleted, an error is triggered, to avoid accidental deletion
• Deletion job can be triggered manually with any cache path as input, to clean outdated data
• Code can safely be added to an existing project pipeline without causing trouble with already existing jobs
• The workflow:rules can be deleted if you already have your own, or updated to match your flow
• The job must be named pages and the artifact must be a public folder to be deployed to GitLab Pages (or you can use the pages:publish keyword)

Conclusion

Given the piece of yaml provided, using it in your pipeline, you should be able to share your GitLab Pages on a per-branch basis, on the path you want, while serving the stable content from the root context.

For any question or remark, please use below comment section 🤓.

If you need information to choose better runner architecture, you can read GitLab Runners topologies: pros and cons.

Illustrations generated locally by Automatic1111 using RevAnimated model with PiratePunkAI and Blindbox LoRA

Further reading

🦊 GitLab CI Optimization: 15+ Tips for Faster Pipelines

Benoit COUETIL 💫 for Zenika ・ Nov 6

#gitlab #devops #pipeline #cicd

🦊 GitLab CI: 10+ Best Practices to Avoid Widespread Anti-patterns

Benoit COUETIL 💫 for Zenika ・ Sep 25

#gitlab #devops #pipeline #cicd

🦊 ChatGPT, If You Please, Make Me a GitLab Jobs Attributes Sorter

Benoit COUETIL 💫 for Zenika ・ Mar 30

#chatgpt #gitlab #ai #python

🦊 GitLab Runners Topologies: Pros and Cons

Benoit COUETIL 💫 for Zenika ・ Feb 7

#gitlab #devops #kubernetes #aws