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

Docker: Ensure you have a Dockerfile in your project.
CircleCI Account: Sign up and link your repository.
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" ]

1. 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:14
jobs:
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-app

workflows:
version: 2
build_and_test:
jobs:
- build

1. 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.

1. Push to Repository

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

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

1. Monitor Build

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

1. 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.