CI/CD with Docker

Continuous Integration and Continuous Deployment (CI/CD) with Docker enables faster, consistent, and automated software delivery. Integrating Docker into CI/CD pipelines ensures consistent environments across development, testing, and production.

Why Use Docker in CI/CD?

Build once, run anywhere — eliminate environment inconsistencies
Test in isolated containers for reliability
Speed up deployment using prebuilt images
Improve rollback capabilities with image versioning

Integrating Docker with Jenkins

Example Jenkins pipeline (Declarative syntax):

pipeline {
    agent any

    stages {
        stage('Build') {
            steps {
                sh 'docker build -t myapp:latest .'
            }
        }
        stage('Test') {
            steps {
                sh 'docker run --rm myapp:latest npm test'
            }
        }
        stage('Push') {
            steps {
                withCredentials([usernamePassword(credentialsId: 'docker-hub-creds',
                                                 usernameVariable: 'USER',
                                                 passwordVariable: 'PASS')]) {
                    sh 'echo $PASS | docker login -u $USER --password-stdin'
                    sh 'docker push myapp:latest'
                }
            }
        }
    }
}

Using Docker with GitHub Actions

Basic workflow to build and push Docker images:

name: CI

on:
  push:
    branches: [ main ]

jobs:
  build:
    runs-on: ubuntu-latest

    steps:
    - uses: actions/checkout@v3

    - name: Log in to Docker Hub
      uses: docker/login-action@v2
      with:
        username: ${{ secrets.DOCKER_USERNAME }}
        password: ${{ secrets.DOCKER_PASSWORD }}

    - name: Build and push
      uses: docker/build-push-action@v3
      with:
        push: true
        tags: myapp:latest

GitLab CI/CD with Docker

Sample .gitlab-ci.yml file for Docker builds:

image: docker:latest

services:
  - docker:dind

variables:
  DOCKER_DRIVER: overlay2

stages:
  - build
  - deploy

build_image:
  stage: build
  script:
    - docker build -t myapp .
    - docker login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" $CI_REGISTRY
    - docker push myapp

Best Practices for Docker CI/CD

Tag images with build numbers or Git SHA for traceability
Run tests inside containers for consistency
Use lightweight base images to speed up builds
Scan Docker images as part of the pipeline
Push only signed or verified images to production registries

Docker enables standardized, reproducible workflows in CI/CD. Whether using Jenkins, GitHub Actions, or GitLab, integrating Docker enhances deployment agility and environment parity.

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