Setup Docker Containers as Build Slaves for Jenkins

Jenkins is one of the most important tools in DevOps. Jenkins is used in the CI/CD stage of DevOps. In this blog, I am going to talk about Setup Docker Containers as Build Slaves for Jenkins.

Steps:

1. Configure docker host for remote connection
2. Write Docker file to Configure Docker Container
3. Configure Docker as a cloud in Jenkins server
4. Create a freestyle job to test

5. checks When Build Start:

• The container will automatically be launched on the docker host machine
• Container destroyed after build completion.

Prerequisite:

One VM with Docker installed also called as Docker Host

How To Install Docker On CentOS 8/RHEL 8

Let's start with practical

Configure docker host for remote connection

The first step is to set up a docker host where the Jenkins server will launch slave containers. Jenkins master connects to docker using APIs. So we need to enable remote connection/remote API for docker. In this article, we will open the connection at port 2376.

• Login to the docker host machine and open the docker service file with path /usr/lib/systemd/system/docker.service . In this file search ExecStart and append -H tcp://192.168.43.177:2376 .

ExecStart=/usr/bin/dockerd -H fd:// -H tcp://192.168.43.177:2376

• reload and restart the docker service.

systemctl daemon-reload
service docker restart

That’s it! All done with Docker Host machine🤩

Step2: Write Dockerfile for slave

There are 3 connection methods for which we have different container environments needed

1. Attach Docker Container

* Docker image must have Java installed.
* Docker image CMD must either be empty or simply sit and wait forever, e.g. /bin/bash.

2. Connect with JNLP[Java Network Launch Protocol]

* Jenkins master has to be accessible over network from the container.
* Docker image must have Java installed.
* Docker image must launch agent.jar by itself or using the EntryPoint Arguments below.

3. Connect with SSH

* The docker container’s mapped SSH port, typically a port on the docker host, has to be accessible over network from the master.
* Docker image must have sshd installed.
* Docker image must have Java installed.
* Log in details configured as per ssh-slaves plugin.

Step3: Configure Docker as a cloud in Jenkins server

Install Plugin Docker Plugin https://plugins.jenkins.io/docker-plugin/

Let's, Configure docker cloud

manage-Jenkins → Manage Nodes and Cloud →Configure Cloud

Add docker as a cloud

Enter docker URI and click on test connection if show you version of docker then docker is configured as cloud

Now we need to provide templates[Details of Image and Connection Method].

Method-1: Attach Docker Container

FROM centos:latest
RUN yum install java git -y
CMD ["/bin/bash"]

build image and push to docker hub repository

docker build -t docker_hub_account_name/image_name:image_version  location_of_docker_file
docker login
docker push image_name:image_version

Create a new job and only we need to pass label

save and start the job. Jenkins Launch the container with the help of a template.

For a conceptual understanding of the other two methods, you can refer to the below article.

Jenkins Configure Master and Slave Nodes

For method 3:

Enable SSH In Container Using Dockerfile And Configure Apache Web Server In Container Using Ansible

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Thank you for reading…😇