Branch discovery configuration in Jenkins - Mini Project: Build & Apply

Branch Discovery Configuration in Jenkins

📖 Scenario: You are setting up a Jenkins job to automatically find and build branches from a Git repository. This helps your team test code changes on different branches without manual setup.

🎯 Goal: Configure a Jenkins pipeline job to discover branches from a Git repository using the Branch Discovery strategy.

📋 What You'll Learn

Create a Jenkins pipeline job configuration with Git SCM

Add branch discovery trait to find branches

Set up a simple pipeline script to print the branch name

Print the discovered branch name as output

💡 Why This Matters

🌍 Real World

Teams use branch discovery in Jenkins to automatically build and test code changes on all branches, improving continuous integration workflows.

💼 Career

Understanding branch discovery is essential for DevOps engineers and Jenkins administrators to maintain efficient CI/CD pipelines.

1

Create initial Jenkins pipeline job configuration

Create a Jenkins pipeline job configuration with a scm block using git and set the url to 'https://github.com/example/repo.git'.

Jenkins

# Create a Jenkins pipeline job configuration with git SCM and URL
pipeline {
    agent any
    stages {
        stage('Setup') {
            steps {
                // Your code here
            }
        }
    }
}

Hint

Use checkout with GitSCM and set the repository URL exactly as given.

2

Add branch discovery trait to configuration

Add a traits list inside checkout configuration with a BranchDiscoveryTrait to enable branch discovery.

Jenkins

pipeline {
    agent any
    stages {
        stage('Setup') {
            steps {
                checkout([
                    $class: 'GitSCM',
                    branches: [[name: '*/main']],
                    userRemoteConfigs: [[
                        url: 'https://github.com/example/repo.git',
                        // Your code here
                    ]]
                ])
            }
        }
    }
}

Hint

Add traits: [[$class: 'BranchDiscoveryTrait']] to enable branch discovery.

3

Add pipeline script to print current branch name

Add a script step inside the Setup stage that prints the current branch name using env.BRANCH_NAME.

Jenkins

pipeline {
    agent any
    stages {
        stage('Setup') {
            steps {
                checkout([
                    $class: 'GitSCM',
                    branches: [[name: '*/main']],
                    userRemoteConfigs: [[
                        url: 'https://github.com/example/repo.git'
                    ]],
                    extensions: [],
                    traits: [[$class: 'BranchDiscoveryTrait']]
                ])
                // Add a script step to print the branch name
                // Your code here
            }
        }
    }
}

Hint

Use script { echo("Current branch is: ${env.BRANCH_NAME}") } to print the branch name.

4

Print the discovered branch name as output

Add a print equivalent in Jenkins pipeline by using echo to display the message "Current branch is: " followed by the branch name stored in env.BRANCH_NAME.

Jenkins

pipeline {
    agent any
    stages {
        stage('Setup') {
            steps {
                checkout([
                    $class: 'GitSCM',
                    branches: [[name: '*/main']],
                    userRemoteConfigs: [[
                        url: 'https://github.com/example/repo.git'
                    ]],
                    extensions: [],
                    traits: [[$class: 'BranchDiscoveryTrait']]
                ])
                script {
                    // Your code here
                }
            }
        }
    }
}

Hint

Use echo("Current branch is: ${env.BRANCH_NAME}") to print the branch name.

Practice

1.

What is the main purpose of branch discovery in Jenkins?

easy

A. To merge branches automatically before building

B. To manually select branches for building

C. To automatically find and build all branches in a repository

D. To delete old branches from the repository

Solution

1. Step 1: Understand branch discovery concept

   Branch discovery is designed to find all branches automatically in a source code repository.

2. Step 2: Identify the purpose in Jenkins

   Jenkins uses branch discovery to keep builds updated without manual intervention.

3. Final Answer:

   To automatically find and build all branches in a repository -> Option C

4. Quick Check:

   Branch discovery = automatic branch finding [OK]

Hint: Branch discovery means Jenkins finds branches automatically [OK]

Common Mistakes:

• Thinking branch discovery requires manual branch selection
• Confusing branch discovery with branch deletion
• Assuming branch discovery merges branches

2.

Which strategyId value in Jenkins branch discovery configuration finds all branches including PRs?

easy

A. 4

B. 2

C. 1

D. 3

Solution

1. Step 1: Recall strategyId meanings

   In Jenkins, strategyId 3 means discover all branches including pull requests.

2. Step 2: Match strategyId to description

   StrategyId 1 is for only branches, 2 is for branches and PRs from origin, 3 includes all branches and PRs, 4 is for PRs only.

3. Final Answer:

   3 -> Option D

4. Quick Check:

   strategyId 3 = all branches + PRs [OK]

Hint: strategyId 3 includes all branches and PRs [OK]

Common Mistakes:

• Confusing strategyId 1 with including PRs
• Using strategyId 4 which only finds PRs
• Assuming strategyId 2 includes PRs

3.

Given this Jenkins branch discovery snippet:

{"strategyId": 1}

Which branches will Jenkins discover?

medium

A. Only branches that are not pull requests

B. All branches including pull requests

C. Only pull request branches

D. No branches will be discovered

Solution

1. Step 1: Understand strategyId 1 meaning

   StrategyId 1 means discover only branches, excluding pull requests.

2. Step 2: Apply to the snippet

   The snippet uses strategyId 1, so Jenkins finds only normal branches, not PRs.

3. Final Answer:

   Only branches that are not pull requests -> Option A

4. Quick Check:

   strategyId 1 = branches only [OK]

Hint: strategyId 1 excludes PRs, finds only branches [OK]

Common Mistakes:

• Assuming strategyId 1 includes PRs
• Thinking strategyId 1 finds no branches
• Confusing strategyId 1 with strategyId 3

4.

You configured Jenkins with {"strategyId": 5} for branch discovery. What is the likely result?

medium

A. Jenkins discovers all branches and PRs correctly

B. Jenkins throws a configuration error or ignores the setting

C. Jenkins discovers only pull requests

D. Jenkins discovers no branches but builds anyway

Solution

1. Step 1: Check valid strategyId values

   Valid strategyId values are 1, 2, 3, and 4. 5 is invalid.

2. Step 2: Predict Jenkins behavior on invalid strategyId

   Jenkins will likely throw an error or ignore the invalid value, causing no discovery.

3. Final Answer:

   Jenkins throws a configuration error or ignores the setting -> Option B

4. Quick Check:

   Invalid strategyId = error or ignore [OK]

Hint: Use only valid strategyId 1-4 to avoid errors [OK]

Common Mistakes:

• Assuming strategyId 5 works like 3 or 4
• Expecting Jenkins to discover branches anyway
• Ignoring configuration errors

5.

You want Jenkins to build only branches that start with feature/ and ignore others. Which branch discovery configuration should you use?

hard

A. Use {"strategyId": 1} with an additional branch filter for feature/*

B. Use {"strategyId": 3} without any filters

C. Use {"strategyId": 2} and disable branch filtering

D. Use {"strategyId": 4} with a filter for feature/*

Solution

1. Step 1: Choose strategyId for branches only

   StrategyId 1 discovers only branches (excluding PRs), suitable for filtering branches.

2. Step 2: Apply branch filter for prefix

   Adding a filter for branches starting with 'feature/' limits builds to those branches only.

3. Final Answer:

   Use {"strategyId": 1} with an additional branch filter for feature/* -> Option A

4. Quick Check:

   strategyId 1 + filter = feature branches only [OK]

Hint: Combine strategyId 1 with branch filter for prefix [OK]

Common Mistakes:

• Using strategyId 3 without filters builds all branches and PRs
• Disabling filters causes all branches to build
• Using strategyId 4 only finds PRs, not branches