Mastering Continuous Integration with CircleCI and Docker Hub

Introduction

Building a Docker image with CircleCI can streamline your CI/CD process by automating the build, test, and deployment of your applications. In this guide, we’ll walk through setting up a CircleCI configuration to build a Docker image.

Prerequisites

1. Docker: Ensure you have a Dockerfile in your project.
2. CircleCI Account: Sign up and link your repository.
3. CircleCI Configuration File: A .circleci/config.yml file in your project root.

Step-by-Step Guide

1. Dockerfile Setup

Ensure your project has a Dockerfile defining the steps to build your Docker image.

dockerfile

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# Example Dockerfile
FROM node:14

# Create app directory
WORKDIR /usr/src/app# Install app dependencies
COPY package*.json ./RUN npm install# Bundle app source
COPY . .EXPOSE 8080
CMD [ "node", "app.js" ]

2. CircleCI Configuration

Create a .circleci/config.yml file in your project root. This file tells CircleCI how to build and test your project.

yaml

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version: 2.1

executors:
  docker-executor:
    docker:
      - image: circleci/node:14jobs:
  build:
    executor: docker-executor
    steps:
      - checkout
      
      - setup_remote_docker:
          version: 20.10.7      - run:
          name: Build Docker image
          command: |
            docker build -t my-app .      - run:
          name: Verify Docker image
          command: |
            docker images my-appworkflows:
  version: 2
  build_and_test:
    jobs:
      - build

3. Breaking Down the Configuration

• Executors: Define the Docker environment for running jobs.
• Jobs: Specify a series of steps to execute.
• Checkout: Check out the code from the repository.
• setup_remote_docker: Enable Docker support in CircleCI.
• Build Docker image: Run docker build command to create the image.
• Verify Docker image: List Docker images to ensure the image was built.

4. Push to Repository

Commit and push your changes to your repository. CircleCI will automatically trigger a build.

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git add .circleci/config.yml
git commit -m "Add CircleCI configuration for Docker build"
git push origin main

5. Monitor Build

Go to the CircleCI dashboard to monitor your build. You should see steps executing as defined in your config.yml.

6. Automate Further Steps (Optional)

You can extend the configuration to push the Docker image to a registry, run tests, or deploy to a cloud service.

Example: Pushing to Docker Hub

yaml

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- run:
          name: Login to Docker Hub
          command: |
            echo $DOCKERHUB_PASS | docker login -u $DOCKERHUB_USER --password-stdin

      - run:
          name: Push Docker image
          command: |
            docker tag my-app $DOCKERHUB_USER/my-app:latest
            docker push $DOCKERHUB_USER/my-app:latest

Ensure you set DOCKERHUB_USER and DOCKERHUB_PASS as environment variables in CircleCI.

Conclusion

By following these steps, you’ve configured CircleCI build Docker image for your project. This setup can be extended to include tests, security scans, or deployment steps, creating a robust CI/CD pipeline.