Jenkins WAR file execution - Mini Project: Build & Apply

Jenkins WAR File Execution

📖 Scenario: You want to run Jenkins on your local machine using the Jenkins WAR file. This is a common way to start Jenkins without installing it as a service. You will learn how to download the WAR file, set a port configuration, run Jenkins, and verify it is running.

🎯 Goal: Learn to execute the Jenkins WAR file with a custom port and confirm Jenkins is running by checking the output.

📋 What You'll Learn

Have Java installed on your machine

Download the Jenkins WAR file

Run Jenkins WAR file on a specified port

Verify Jenkins startup output

💡 Why This Matters

🌍 Real World

Running Jenkins from the WAR file is a quick way to start Jenkins without full installation. It is useful for testing or temporary setups.

💼 Career

Understanding how to run Jenkins WAR files helps DevOps engineers manage Jenkins servers and automate CI/CD pipelines efficiently.

1

Download the Jenkins WAR file

Create a variable called jenkins_war_url and set it to the exact string "https://get.jenkins.io/war-stable/latest/jenkins.war".

Jenkins

# Create a variable called jenkins_war_url with the Jenkins WAR download URL
# Your code here

Hint

Use a string variable to store the exact Jenkins WAR file URL.

2

Set the Jenkins server port

Create a variable called jenkins_port and set it to the integer 8080 to specify the port Jenkins will run on.

Jenkins

jenkins_war_url = "https://get.jenkins.io/war-stable/latest/jenkins.war"
# Create a variable called jenkins_port and set it to 8080
# Your code here

Hint

Use an integer variable to hold the port number 8080.

3

Run the Jenkins WAR file with the port configuration

Write a command string called run_command that uses java -jar jenkins.war --httpPort=8080 to run Jenkins on the port stored in jenkins_port. Use an f-string to insert the port number.

Jenkins

jenkins_war_url = "https://get.jenkins.io/war-stable/latest/jenkins.war"
jenkins_port = 8080
# Create a run_command string to run Jenkins WAR on the port using java -jar
# Your code here

Hint

Use an f-string to insert the port number variable into the command string.

4

Print the Jenkins run command

Write a print statement to display the exact run_command string.

Jenkins

jenkins_war_url = "https://get.jenkins.io/war-stable/latest/jenkins.war"
jenkins_port = 8080
run_command = f"java -jar jenkins.war --httpPort={jenkins_port}"
# Print the run_command string
# Your code here

Hint

Use print(run_command) to show the command that runs Jenkins.

Practice

1. What does running java -jar jenkins.war do in Jenkins?

easy

A. Deletes Jenkins configuration files

B. Installs Jenkins permanently on the system

C. Updates Jenkins to the latest version

D. Starts Jenkins server without installing it

Solution

1. Step 1: Understand the command purpose

   The command java -jar jenkins.war runs the Jenkins server directly from the WAR file without installation.

2. Step 2: Differentiate from installation

   This method does not install Jenkins permanently but starts it temporarily for use or testing.

3. Final Answer:

   Starts Jenkins server without installing it -> Option D

4. Quick Check:

   Run WAR file = Start Jenkins temporarily [OK]

Hint: WAR file runs Jenkins without install, just start it [OK]

Common Mistakes:

• Thinking it installs Jenkins permanently
• Confusing it with Jenkins update command
• Assuming it deletes files

2. Which command correctly starts Jenkins on port 9090 using the WAR file?

easy

A. java -jar jenkins.war --httpPort=9090

B. java -jar jenkins.war -p 9090

C. java -jar jenkins.war --port 9090

D. java -jar jenkins.war -httpPort 9090

Solution

1. Step 1: Recall Jenkins WAR port option syntax

   The correct option to specify port is --httpPort=9090 when running the WAR file.

2. Step 2: Check other options for correctness

   Options B, C, and D use incorrect flags or syntax not recognized by Jenkins WAR execution.

3. Final Answer:

   java -jar jenkins.war --httpPort=9090 -> Option A

4. Quick Check:

   Use --httpPort=number to set port [OK]

Hint: Use --httpPort=PORT to set Jenkins port [OK]

Common Mistakes:

• Using -p or --port which Jenkins WAR does not recognize
• Missing equal sign in option
• Using single dash for long option

3. What will be the output if you run java -jar jenkins.war --httpPort=8080 when port 8080 is already in use?

medium

A. Error: Address already in use, Jenkins fails to start

B. Jenkins automatically switches to port 8081

C. Jenkins starts successfully on port 8080

D. Jenkins ignores the port option and uses default

Solution

1. Step 1: Understand port conflict behavior

   If the specified port (8080) is busy, Jenkins cannot bind to it and will fail to start with an error.

2. Step 2: Check Jenkins automatic port fallback

   Jenkins WAR does not automatically switch ports; it requires manual change if port is busy.

3. Final Answer:

   Error: Address already in use, Jenkins fails to start -> Option A

4. Quick Check:

   Port busy = Jenkins start error [OK]

Hint: Busy port causes Jenkins start error, no auto-switch [OK]

Common Mistakes:

• Assuming Jenkins auto-switches ports
• Thinking Jenkins ignores port option
• Believing Jenkins starts anyway on busy port

4. You ran java -jar jenkins.war --httpPort=abc and Jenkins did not start. What is the likely cause?

medium

A. Jenkins requires root privileges to start

B. Jenkins WAR file is corrupted

C. Invalid port number format causes startup failure

D. Java is not installed on the system

Solution

1. Step 1: Analyze the port option value

   The port option --httpPort=abc uses non-numeric characters, which is invalid for a port number.

2. Step 2: Understand Jenkins port validation

   Jenkins expects a numeric port; invalid format causes startup failure with error.

3. Final Answer:

   Invalid port number format causes startup failure -> Option C

4. Quick Check:

   Port must be numeric for Jenkins to start [OK]

Hint: Port must be a number, not letters [OK]

Common Mistakes:

• Blaming Jenkins WAR file corruption
• Assuming Java is missing without checking
• Thinking root privileges are always needed

5. You want to run Jenkins WAR file on port 7070 and also specify a custom Jenkins home directory at /data/jenkins_home. Which command is correct?

hard

A. java -jar jenkins.war --httpPort=7070 --jenkinsHome=/data/jenkins_home

B. java -Djenkins.home=/data/jenkins_home -jar jenkins.war --httpPort=7070

C. java -jar jenkins.war --httpPort=7070 --jenkins.home=/data/jenkins_home

D. java -jar jenkins.war --httpPort=7070 -DjenkinsHome=/data/jenkins_home

Solution

1. Step 1: Set port option correctly

   The port is set with --httpPort=7070, which is correct syntax.

2. Step 2: Set Jenkins home directory properly

   Jenkins home is set via Java system property -Djenkins.home=path, not as a command option.

3. Step 3: Verify option correctness

   The correct command places the -Djenkins.home= option before -jar to set the system property properly.

4. Final Answer:

   java -Djenkins.home=/data/jenkins_home -jar jenkins.war --httpPort=7070 -> Option B

5. Quick Check:

   Use -Djenkins.home=PATH for custom Jenkins home [OK]

Hint: Use -Djenkins.home=PATH to set Jenkins home [OK]

Common Mistakes:

• Using --jenkinsHome or --jenkins.home as options
• Confusing Java system properties with command options
• Missing -D prefix for system properties
• Placing -D option after -jar which is incorrect