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CI/CD & Container Automation

Docker in CI/CD

Learn how Docker is used in CI/CD pipelines to build, test, package, publish, and deploy applications using portable container images.

Level: Beginner to Intermediate
Topic: Docker & CI/CD
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Docker CI/CD Workflow

Build Once, Deploy Consistently

Source Code

Build Docker Image

Run Tests

Scan Image

Push to Registry

Deploy Container

Introduction

Why use Docker in CI/CD?

Docker allows applications and their dependencies to be packaged into portable container images. These images can be built and tested automatically inside CI/CD pipelines.

Using containers helps teams create consistent environments for development, testing, and deployment. The same application image can move through multiple stages of the software delivery lifecycle.

A typical Docker-based CI/CD workflow builds an image, runs tests, validates or scans the image, publishes it to a registry, and deploys the required version.

Core Concepts

Understanding Docker in CI/CD

Docker can provide reproducible build environments and portable application packages that fit naturally into automated CI/CD workflows.

01

Containerized Build Environment

Docker provides isolated and reproducible environments for building and testing applications inside CI/CD pipelines.

Key Topics

  • • Reproducible builds
  • • Isolated environments
  • • Build dependencies
  • • Consistent execution
02

Docker Images

A Docker image packages an application together with its runtime, dependencies, libraries, and configuration required to run it.

Key Topics

  • • Dockerfile
  • • Image layers
  • • Image tags
  • • Build automation
03

Containers

Containers are runnable instances of Docker images that can be used for testing applications and running workloads in different environments.

Key Topics

  • • Application testing
  • • Isolation
  • • Runtime environments
  • • Portability
04

Container Registry

A container registry stores and distributes Docker images so CI/CD pipelines and deployment platforms can retrieve the correct application version.

Key Topics

  • • Push images
  • • Pull images
  • • Version tags
  • • Image distribution

Docker Workflow

Main components

Dockerfile

Defines the instructions used to create a Docker image for your application.

Docker Build

Creates a Docker image from the source code and Dockerfile instructions.

Docker Image

A portable package containing the application and the required runtime environment.

Docker Container

A running instance of a Docker image used to execute and test an application.

Container Registry

Stores Docker images so they can be shared between CI/CD pipelines and deployment environments.

CI/CD Platform

Automates the workflow that builds, tests, scans, publishes, and deploys containerized applications.

Containerization

Build an application with Docker

A Dockerfile contains instructions that define how an application image should be created. The CI/CD pipeline can automatically run the Docker build process whenever changes are pushed.

The resulting image can then be used for testing and deployment, helping ensure that the same application package moves through the delivery workflow.

Example Dockerfile

FROM node:22-alpine

WORKDIR /app

COPY package*.json ./

RUN npm ci

COPY . .

RUN npm run build

EXPOSE 3000

CMD ["npm", "start"]

Pipeline Workflow

How Docker works in a CI/CD pipeline

Docker can be integrated into different CI/CD platforms to automate image creation, testing, publishing, and deployment.

01

Source

A developer pushes application code and Docker configuration to the source repository.

02

Build

The CI/CD pipeline builds the application and creates a Docker image using the Dockerfile.

03

Test

Automated tests and validation can run against the application or the generated container image.

04

Scan

The image can be checked for vulnerabilities, configuration problems, and other security issues.

05

Push

The validated Docker image is tagged and pushed to a container registry.

06

Deploy

The deployment platform pulls the required image version and runs the updated application.

Pipeline Example

Docker image automation

The following example shows the general idea of a CI/CD workflow that builds a Docker image, runs tests, and then pushes the image to a registry.

The exact configuration will depend on the CI/CD platform, runner, registry, security requirements, and deployment environment you use.

Example CI/CD Configuration

stages:
  - build
  - test
  - push

build-image:
  stage: build
  script:
    - docker build -t my-app:$CI_COMMIT_SHA .

test-image:
  stage: test
  script:
    - docker run --rm my-app:$CI_COMMIT_SHA npm test

push-image:
  stage: push
  script:
    - docker tag my-app:$CI_COMMIT_SHA registry.example.com/my-app:$CI_COMMIT_SHA
    - docker push registry.example.com/my-app:$CI_COMMIT_SHA

Use Cases

What can Docker automate in CI/CD?

Automated Application Builds

Build application images automatically whenever developers push changes to the repository.

Consistent Testing

Run tests inside consistent container environments with the required dependencies.

Image Publishing

Automatically tag and publish validated images to a container registry.

Cloud Deployment

Deploy the same tested container image across development, staging, and production environments.

Kubernetes Deployment

Use CI/CD pipelines to build images and deploy updated workloads to Kubernetes clusters.

Microservices Delivery

Build, test, version, and deploy individual services independently as container images.

Learning Roadmap

How to learn Docker for CI/CD

Follow these steps to move from Docker fundamentals to building automated container delivery pipelines.

Step 1

Learn Docker Fundamentals

Understand Docker images, containers, Dockerfiles, registries, volumes, and networking.

Step 2

Containerize an Application

Create a Dockerfile and build a Docker image for a simple application.

Step 3

Build Images in CI

Configure a CI/CD pipeline to automatically build Docker images whenever code changes.

Step 4

Test Containers

Run automated tests and validation against the application or generated container image.

Step 5

Publish Images

Tag and push validated Docker images to a container registry.

Step 6

Automate Deployment

Use the container image in deployment workflows for servers, cloud platforms, or Kubernetes.

Best Practices

Docker CI/CD best practices

Use Small Base Images

Choose an appropriate and minimal base image to reduce unnecessary dependencies and improve portability.

Use Multi-Stage Builds

Separate build dependencies from the final runtime image when appropriate to keep production images smaller.

Tag Images Clearly

Use meaningful and traceable image tags instead of relying only on a single mutable tag.

Use .dockerignore

Exclude unnecessary files from the Docker build context to improve build efficiency and avoid including unwanted files.

Build and Test Automatically

Use your CI/CD pipeline to automatically build and test images whenever important code changes are introduced.

Protect Registry Credentials

Store registry credentials and other secrets using the CI/CD platform's protected secret or variable mechanisms.

Continue Learning

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Next Step

Start building Docker-powered CI/CD pipelines

Practice containerizing applications, building Docker images, running automated tests, publishing images to registries, and deploying the same validated image across environments.

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