Master-agent architecture in Jenkins - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Jenkins Master-Agent Communication

In Jenkins master-agent architecture, what is the primary role of the agent?

A Execute build jobs assigned by the master

B Manage user authentication and authorization

C Store build artifacts centrally

D Schedule build jobs on the master node

💡 Hint

Think about which component actually runs the build tasks.

The agent is responsible for running the build jobs sent by the master. The master coordinates and schedules jobs but does not execute them directly.

💻 Command Output

intermediate

Agent Connection Status Command Output

What is the output of the following Jenkins CLI command when the agent is connected and online?

java -jar jenkins-cli.jar -s http://jenkins.example.com list-agents

A Error: Command not found

B

agent1  Online  Building
agent2  Online  Idle

C

agent1  Online  Idle
agent2  Offline  Disconnected

D

agent1  Offline  Disconnected
agent2  Offline  Disconnected

💡 Hint

Look for the status that indicates the agent is connected and ready.

The 'Online' status means the agent is connected and ready. 'Idle' means it is not currently running a job.

❓ Configuration

advanced

Configuring Agent Launch Method

Which configuration snippet correctly sets a Jenkins agent to launch via SSH with the hostname 'agent-host' and user 'jenkins-user'?

A

<slave>
  <name>agent1</name>
  <launcher class="hudson.plugins.sshslaves.SSHLauncher">
    <host>agent-host</host>
    <port>22</port>
    <credentialsId>jenkins-user</credentialsId>
  </launcher>
</slave>

B

<slave>
  <name>agent1</name>
  <launcher class="hudson.slaves.JNLPLauncher"/>
  <host>agent-host</host>
  <user>jenkins-user</user>
</slave>

C

<agent>
  <name>agent1</name>
  <launchMethod>SSH</launchMethod>
  <host>agent-host</host>
  <user>jenkins-user</user>
</agent>

D

<slave>
  <name>agent1</name>
  <launcher class="hudson.plugins.sshslaves.SSHLauncher">
    <hostname>agent-host</hostname>
    <port>22</port>
    <user>jenkins-user</user>
  </launcher>
</slave>

💡 Hint

Check the XML tags and attribute names for SSHLauncher configuration.

Option A uses the correct XML structure and tag names for SSHLauncher in Jenkins agent configuration.

❓ Troubleshoot

advanced

Agent Connection Failure Diagnosis

A Jenkins agent fails to connect to the master and shows 'Disconnected' status. Which of the following is the most likely cause?

A The Jenkins master URL is set to HTTP instead of HTTPS

B The master node is running out of disk space

C The agent has too many executors configured

D The agent's JNLP secret key is incorrect or missing

💡 Hint

Consider what is required for secure agent authentication.

The JNLP secret key is used to authenticate the agent to the master. If it is wrong or missing, the agent cannot connect.

🔀 Workflow

expert

Master-Agent Job Execution Flow

Arrange the following steps in the correct order for a Jenkins job executed on an agent:

A 2,1,3,4

B 1,2,3,4

C 1,3,2,4

D 3,1,2,4

💡 Hint

Think about the logical flow from scheduling to execution to reporting.

The master first schedules and sends the job, the agent runs it, then reports status, and finally the master updates the job record.