Milestone step for concurrency in Jenkins - Mini Project: Build & Apply

Using Milestone Step for Concurrency Control in Jenkins Pipelines

📖 Scenario: You are managing a Jenkins pipeline that deploys applications. Sometimes multiple builds run at the same time, but you want to make sure only the latest build proceeds past a certain point to avoid conflicts.

🎯 Goal: Build a Jenkins pipeline script that uses the milestone step to control concurrency, allowing only the newest build to continue past the milestone.

📋 What You'll Learn

Create a Jenkins pipeline script with a milestone step

Add a stage before the milestone to simulate build preparation

Add a stage after the milestone to simulate deployment

Use the milestone step with an explicit ordinal number

Print messages to show the pipeline progress

💡 Why This Matters

🌍 Real World

In real Jenkins pipelines, the milestone step helps prevent multiple builds from deploying at the same time, avoiding conflicts and wasted resources.

💼 Career

Understanding concurrency control in Jenkins pipelines is important for DevOps engineers to maintain stable and efficient CI/CD workflows.

1

Create the initial Jenkins pipeline with a preparation stage

Write a Jenkins pipeline script that defines a pipeline block with an agent any and a stage named 'Preparation'. Inside this stage, add a steps block that prints 'Starting build preparation'.

Jenkins

pipeline {
    agent any
    stages {
        stage('Preparation') {
            steps {
                // Your code here
            }
        }
    }
}

Hint

Use echo inside steps to print the message.

2

Add a milestone step with ordinal 1 after preparation

Add a new stage named 'Milestone' after the 'Preparation' stage. Inside its steps block, add a milestone 1 step to mark the concurrency control point.

Jenkins

pipeline {
    agent any
    stages {
        stage('Preparation') {
            steps {
                echo 'Starting build preparation'
            }
        }
        stage('Milestone') {
            steps {
                // Your code here
            }
        }
    }
}

Hint

The milestone step takes an integer ordinal to identify the milestone.

3

Add a deployment stage after the milestone

Add a stage named 'Deploy' after the 'Milestone' stage. Inside its steps block, add an echo statement that prints 'Deploying application'.

Jenkins

pipeline {
    agent any
    stages {
        stage('Preparation') {
            steps {
                echo 'Starting build preparation'
            }
        }
        stage('Milestone') {
            steps {
                milestone 1
            }
        }
        stage('Deploy') {
            steps {
                // Your code here
            }
        }
    }
}

Hint

Use echo to print the deployment message inside the Deploy stage.

4

Print a final message after deployment

Add a post block to the pipeline with a always condition. Inside it, add a script block that prints 'Pipeline finished' using echo.

Jenkins

pipeline {
    agent any
    stages {
        stage('Preparation') {
            steps {
                echo 'Starting build preparation'
            }
        }
        stage('Milestone') {
            steps {
                milestone 1
            }
        }
        stage('Deploy') {
            steps {
                echo 'Deploying application'
            }
        }
    }
    // Your code here
}

Hint

The post block runs after all stages. Use always to run regardless of success or failure.

Practice

1. What is the main purpose of the milestone step in a Jenkins pipeline?

easy

A. To allow only the latest pipeline run to continue past a certain point

B. To trigger a new pipeline run automatically

C. To send notifications when a build fails

D. To archive build artifacts for later use

Solution

1. Step 1: Understand the role of the milestone step

   The milestone step is designed to control concurrency by ensuring only the newest pipeline run proceeds beyond the milestone point.

2. Step 2: Compare with other pipeline steps

   Other steps like triggering builds or sending notifications do not control concurrency like milestone does.

3. Final Answer:

   To allow only the latest pipeline run to continue past a certain point -> Option A

4. Quick Check:

   Milestone controls concurrency = B [OK]

Hint: Milestone lets only the newest run pass a checkpoint [OK]

Common Mistakes:

• Confusing milestone with notification steps
• Thinking milestone triggers builds
• Assuming milestone archives artifacts

2. Which of the following is the correct syntax to add a milestone step with label "BuildCheckpoint" in a Jenkins declarative pipeline?

easy

A. milestone label: 'BuildCheckpoint'

B. milestone('BuildCheckpoint')

C. milestone label = 'BuildCheckpoint'

D. milestone: 'BuildCheckpoint'

Solution

1. Step 1: Recall the correct milestone syntax

   The milestone step uses named parameters with the syntax: milestone label: 'LabelName'.

2. Step 2: Identify syntax errors in other options

   Options B, C, and D have incorrect syntax such as missing named parameter format or wrong punctuation.

3. Final Answer:

   milestone label: 'BuildCheckpoint' -> Option A

4. Quick Check:

   Correct milestone syntax uses label: 'name' [OK]

Hint: Use named parameter syntax: milestone label: 'Name' [OK]

Common Mistakes:

• Using parentheses instead of named parameters
• Using equal sign instead of colon
• Omitting the label keyword

3. Given this Jenkins pipeline snippet:

stage('Test') {
  steps {
    milestone label: 'TestStart'
    echo 'Running tests'
  }
}

// Two pipeline runs start quickly one after another

What happens to the first pipeline run when the second run reaches the same milestone?

medium

A. The first run continues normally alongside the second

B. The second run waits until the first run finishes

C. The first run is aborted and only the second run continues past the milestone

D. Both runs are aborted at the milestone

Solution

1. Step 1: Understand milestone concurrency behavior

   When multiple runs reach the same milestone label, Jenkins allows only the latest run to proceed and aborts older runs at that point.

2. Step 2: Apply this to the scenario

   The second run reaching 'TestStart' milestone causes the first run to abort at that milestone, so only the second run continues.

3. Final Answer:

   The first run is aborted and only the second run continues past the milestone -> Option C

4. Quick Check:

   Milestone aborts older runs = D [OK]

Hint: Milestone aborts older runs, keeps newest only [OK]

Common Mistakes:

• Thinking both runs continue
• Assuming second run waits
• Believing both runs abort

4. You added a milestone step in your Jenkins pipeline but it does not seem to abort older runs as expected. Which of the following is the most likely cause?

medium

A. The pipeline is missing the agent block

B. The milestone step is placed after all stages have completed

C. The milestone label is not unique and is reused in multiple places

D. The Jenkins server is offline

Solution

1. Step 1: Check milestone placement

   The milestone step is most likely placed after all stages have completed. This makes it ineffective because older runs finish before a newer run can reach the milestone to trigger aborts.

2. Step 2: Evaluate other options

   Label reuse affects log clarity but not concurrency control (ordinals matter). Missing agent prevents runs entirely. Server offline stops everything.

3. Final Answer:

   The milestone step is placed after all stages have completed -> Option B

4. Quick Check:

   Milestone placement before completion critical = A [OK]

Hint: Place milestone before critical/protected sections [OK]

Common Mistakes:

• Placing milestone after all stages
• Blaming unrelated pipeline syntax
• Assuming server offline causes milestone issues

5. You want to ensure that only the latest run of your Jenkins pipeline proceeds past the "Deploy" stage, aborting any previous runs stuck at that point. How should you use the milestone step to achieve this?

hard

A. Use milestone label: 'Deploy' only in the first stage

B. Place milestone label: 'Deploy' at the end of the Deploy stage

C. Place milestone label: 'Deploy' in every stage before Deploy

D. Place milestone label: 'Deploy' at the start of the Deploy stage

Solution

1. Step 1: Identify where to place milestone for concurrency control

   To abort older runs before deploying, place the milestone step at the start of the Deploy stage so only the newest run proceeds.

2. Step 2: Understand why other placements fail

   Placing milestone at the end or in other stages won't stop older runs before deployment. Using it only in the first stage doesn't control concurrency at Deploy.

3. Final Answer:

   Place milestone label: 'Deploy' at the start of the Deploy stage -> Option D

4. Quick Check:

   Milestone at stage start controls concurrency there [OK]

Hint: Put milestone at stage start to block old runs [OK]

Common Mistakes:

• Placing milestone too late in the stage
• Using milestone in unrelated stages
• Not placing milestone at all