This setup provides maximum flexibility, as Jenkins can automatically adjust the number of agents (slaves) based on the current workload. Let’s walk through how to configure Jenkins to use dynamically provisioned Docker agents.

Configuring Dynamically Provisioned Docker Agents

To set up dynamic Docker agents, you'll first need to install the Docker plugin. Here’s how you can do it:

  1. Go to Manage Jenkins.
  2. Click on Manage Plugins.

In the Available tab, search for the Docker plugin and install it.

Once installed, you can proceed with the following configuration steps:

  1. Navigate to Manage Jenkins and click on Configure System.
  2. Scroll down to the Cloud section at the bottom of the page.
  3. Click Add a new cloud and select Docker.
  4. Now, provide the necessary Docker agent details:
    • Docker URL: This is the URL of the Docker host where the agents will run.
    • Credentials: If the Docker host requires authentication, enter the relevant credentials.

If you plan to use the same Docker host where Jenkins is running, make sure that the Docker daemon is set to listen on the docker0 network interface. You can modify the Docker configuration by editing /lib/systemd/system/docker.service as follows:

ExecStart=/usr/bin/dockerd -H 0.0.0.0:2375 -H fd://

Adding a Docker Agent Template

After setting up the Docker host, follow these steps to configure the Docker agent template:

  1. Click on Add Docker Template and select Docker Template.
  2. Fill out the details for the Docker slave image. Common parameters include:
    • Docker Image: One popular option is the evarga/jenkins-slave image from the Jenkins community.
    • Instance Capacity: Set this to define the maximum number of Docker agents running concurrently (e.g., 10).

Fine-Tuning the Setup

Each build will now trigger the creation of a new Docker container based on the specified slave image. This approach provides several benefits:

  • Scalability: Agents are spun up only when needed, allowing Jenkins to automatically handle high build loads without manually adding agents.
  • Consistency: All agents are identical in configuration, running inside Docker containers. This ensures consistent build environments for all jobs.

By leveraging this setup, you achieve dynamic scalability while ensuring that your Jenkins environment remains lightweight, efficient, and highly responsive to changes in build demand.