GitLab Advanced CI/CD - Hands-On Lab: Configurations for Complex Processes

This Hands-On Guide walks you through common configurations for complex CI/CD processes

In this lab we will analyze more complex merge processes, looking specifically at merge trains and merge conflicts. First, we will start with merge trains.

Estimate time to complete: 15 minutes

Objectives

Understand the concept of merge trains and their benefits
Enable merge trains in a GitLab project
Create and run a merge train
Identify and resolve merge conflicts in GitLab
Practice handling conflicting merge requests

Task A. Enabling Merge Trains

To enable a merge train in your project, in the left sidebar, select Settings > Merge requests.
Under Merge options, click the options Enable merged results pipeline, Pipelines must succeed, and Enable merge trains.
At the bottom of the section, select Save changes.

Task B. Running a merge train

To demonstrate a merge train, let’s create a purposefully long CI/CD job.

Navigate to your project repository.
Select the .gitlab-ci.yml file.
In your existing CI/CD file, add the following job to your pipeline:
```
pause:
  stage: test
  script:
    - sleep 4m
```
Add in the following rules to ensure jobs run on merge request pipelines:

workflow:
      auto_cancel:
        on_job_failure: all
      rules:
        - if: $CI_PIPELINE_SOURCE == 'merge_request_event'
        - if: $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH

The current pipeline should look like this:

  stages:
    - deps
    - test
    
  workflow:
    auto_cancel:
      on_job_failure: all
    rules:
      - if: $CI_PIPELINE_SOURCE == 'merge_request_event'
      - if: $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH

  default:
    image: node:latest

  .artifactdef: &artifactdef
    artifacts:
      when: always
      reports:
        junit: junit.xml

  .install deps: &cachedef
    stage: deps
    script:
      - npm install jest-junit
    cache:
      key: $CI_COMMIT_REF_SLUG
      paths:
        - node_modules

  test binarysearch:
    before_script:
      - npm install -g jest
    script:
      - jest --ci --testResultsProcessor=jest-junit binarysearch.test.js
    <<: [*artifactdef, *cachedef]

  test linearsearch:
    before_script:
      - npm install -g jest
    script:
      - jest --ci --testResultsProcessor=jest-junit linearsearch.test.js
    <<: [*artifactdef, *cachedef]
    
  pause:
    stage: test
    script:
      - sleep 4m

Adding this job will ensure that you have enough time to create two merge requests.

To start, create your two merge requests. For the first merge request:

Select Code > Branches.
Select New branch.
Add the branch name train.
Leave all other options as default and select Create branch.
Select the README.md file and add some changes to it.
Select Create merge request.
Leave all options as default and select Create merge request.

For the second merge request:

Select Code > Branches.
Select New branch.
Add the branch name train-2.
Leave all other options as default and select Create branch.
Select the README.md file and add some changes to it. Try making different changes to the file than the ones you did in the previous branch.
Select Create merge request.
Leave all options as default and select Create merge request.

Now that both merge requests have been created:

Set them both to auto-merge. You will see a message stating Set by your user to start a merge train when all merge checks pass.
Await the completion of your merge requests and verify that they merge successfully.

Task C. Merge Conflicts

When multiple users work on a project at the same time, merge conflicts are often inevitable. In this lab, you will learn how to handle merge requests in your project.

Remove the pause job from your CI/CD project to avoid slowdowns. Right now, your file will look like this:

stages:
  - deps
  - test

workflow:
  auto_cancel:
    on_job_failure: all

default:
  image: node:latest

.artifactdef: &artifactdef
  artifacts:
    when: always
    reports:
      junit: junit.xml

.install deps: &cachedef
  stage: deps
  script:
    - npm install jest-junit
  cache:
    key: $CI_COMMIT_REF_SLUG
    paths:
      - node_modules

test binarysearch:
  before_script:
    - npm install -g jest
  script:
    - jest --ci --testResultsProcessor=jest-junit binarysearch.test.js
  <<: [*artifactdef, *cachedef]

test linearsearch:
  before_script:
    - npm install -g jest
  script:
    - jest --ci --testResultsProcessor=jest-junit linearsearch.test.js
  <<: [*artifactdef, *cachedef]

Now, let’s create two merge requests that conflict:

Select Code > Branches.
Select New branch.
Add the branch name conflict.
Leave all other options as default and select Create branch.

Select the index.js file. At the top of the file, add a comment to describe the function. An example comment is below.

// This method will create a binary search finding the value in lin log(n) time
module.exports.binarySearch = function binarySearch(arr, val) { 
    let start = 0; 
    let end = arr.length - 1; 
    while (start <= end) { 
        let mid = Math.floor((start + end) / 2); 
        if (arr[mid] === val) { 
            return mid; 
        } 
        if (val < arr[mid]) { 
            end = mid - 1; 
        } else { 
            start = mid + 1; 
        } 
    } 
    return -1; 
}

Commit this code to the branch and create a new merge request from it. After you do this, create a new branch:
Select Code > Branches.
Select New branch.
Add the branch name conflict-2.
Leave all other options as default and select Create branch.

Select the index.js file. At the top of the file, add a different comment to describe the function. An example comment is below:

//A binary search will search a list in log(n) time
module.exports.binarySearch = function binarySearch(arr, val) { 
    let start = 0; 
    let end = arr.length - 1; 
    while (start <= end) { 
        let mid = Math.floor((start + end) / 2); 
        if (arr[mid] === val) { 
            return mid; 
        } 
        if (val < arr[mid]) { 
            end = mid - 1; 
        } else { 
            start = mid + 1; 
        } 
    } 
    return -1; 
}

Commit this code to the branch and create a new merge request from it.
Return to your conflict merge request and merge it into the repository.
After it merges, navigate to your conflict-2 merge request. You will now see that the merge is blocked, stating Merge conflicts must be resolved.
Select the option Resolve conflicts. You will have the option to select either using the code in the current merge request, or using the code in main.
Select your preferred option, then select Commit to source branch.

After doing this, you will now be able to merge your merge request.

Lab Guide Complete

You have completed this lab exercise. You can view the other lab guides for this course.

Suggestions?

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Last modified December 13, 2024: Remove trailing spaces (a4c83fb3)

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