How to Set Up Multi-Branch CI/CD with Docker, GitLab, and Jenkins for PHP Projects

Background

When a project grows and multiple developers work on different features, using a single branch for development, testing, and deployment leads to code conflicts, accidental breakages, and interference between concurrent test runs. A multi‑branch deployment strategy isolates each developer’s code in its own test environment.

Required Tools

Linux (CentOS 8 as used in the example)

GitLab for source‑code management

Jenkins for continuous integration and deployment

Docker for containerizing GitLab, Jenkins, and the web application

Nginx as the web server/reverse proxy

PHP runtime

Git command‑line client

All tools are installed via yum on a system that already has the yum package manager.

Step‑by‑Step Setup

1. Install Docker

yum install docker

2. Deploy GitLab

docker pull gitlab-ce

docker run --name gitlab -p 443:443 -p 80:80 -p 22:22 \
  -v /data/www/gitlab/config:/etc/gitlab \
  -v /data/www/gitlab/logs:/var/log/gitlab \
  -v /data/www/gitlab/data:/var/opt/gitlab \
  gitlab/gitlab-ce /bin/bash

After the container starts, access http://localhost to verify GitLab.

3. Build a Custom Jenkins Image

The official Jenkins image lacks Composer, PHP, and Git, which are needed for the PHP project. The process is:

Pull a CentOS base image: docker pull centos:latest Create a container from the base image:

docker run -idt --name jenkins docker.io/centos /bin/bash

Enter the container: docker exec -it jenkins /bin/bash Install Java, PHP, Composer, and Git via yum and the Composer installer script.

Install the official Jenkins package:

wget -O /etc/yum.repos.d/jenkins.repo https://pkg.jenkins.io/redhat/jenkins.repo
rpm --import https://pkg.jenkins.io/redhat/jenkins.io.key
yum install jenkins

Configure Jenkins by editing /etc/sysconfig/jenkins (set JENKINS_HOME, JENKINS_USER, JENKINS_PORT), then start it: service jenkins start Make the container start automatically by adding a startup script ( jenkins.sh) to /etc/rc.d/rc.local and committing the container as a new image:

chmod +x /usr/local/jenkins/jenkins.sh
 echo "/usr/local/jenkins/jenkins.sh" >> /etc/rc.d/rc.local
docker commit -m 'Jenkins with docker/composer/git/php' jenkins jenkins:latest

Run the new Jenkins container with port mappings and Docker socket volume:

docker run -idt --name jenkins -p 8080:8080 -p 50000:50000 \
  -v /var/run/docker.sock:/var/run/docker.sock \
  -v /data/www/jenkins/jenkins_home:/var/lib/jenkins:rw \
  jenkins /bin/bash

4. Create a GitLab Project

Generate an access token in GitLab (used later by Jenkins).

Create a new repository.

Configure a Webhook that triggers on push events.

5. Configure Jenkins Jobs

Install the following plugins to enable GitLab integration:

GitLab Plugin

GitLab Hook Plugin

GitLab API Plugin

ruby-runtime

Set up the GitLab connection in Jenkins using the access token, then create a pipeline job that pulls the code from the GitLab repository, builds the PHP project (e.g., runs composer install), and deploys it to a dedicated Docker container or directory.

Result

After completing the steps above, each developer can push code to their own branch in GitLab, Jenkins will automatically build and deploy that branch to an isolated test environment, eliminating interference between concurrent feature tests.