Docker has revolutionized the way we develop, ship, and run applications. However, one common challenge developers face is the size of Docker images. Large images can be slow to download and take up more storage space, leading to inefficiencies in the development and deployment processes. Fortunately, docker multistage builds help you create smaller, more efficient container images with better caching and enhanced security. In other words, you can say that docker multistage builds are ideal for those who have found it challenging to optimize Dockerfiles while ensuring they remain clear and easy to manage.
In this article, we’ll explore some advanced techniques that go beyond the basic practice of transferring files between the build and runtime stages. These tips will help you fully leverage the power of docker multistage builds. If you're unfamiliar with how multistage docker files work, it’s a good idea to start with an introductory guide first.
WHAT IS DOCKER MULTISTAGE BUILD?
To understand the Docker Multistage build concept, first, you should know about what is a docker image. A Docker image is a portable package that includes all the necessary components to run an application. To create a docker image of an application, all instructions specified in Dockerfiles, ensure the software runs quickly and reliably.
In a Docker Multistage build, you can use dockerfile multiple FROM statements, each starting a new build stage and potentially using a different base image. This approach allows you to pass artefacts from one stage to another, excluding any unnecessary components from the final image.
WHY USE DOCKER MULTISTAGE BUILD?
Here are some advantages of using Docker's multistage build:
Reduced Container Image Size:By including only the necessary components in the final image, docker multistage builds help eliminate unnecessary files and dependencies, resulting in a smaller image size.
Enhanced Security: A smaller image with fewer components reduces the attack surface, improving the overall security of your application.
Easier Maintenance: Docker Multistage builds separate the build and runtime environments, making Dockerfiles simpler to understand and maintain.
HOW TO USE DOCKER MULTISTAGE BUILDS? (STEP-BY-STEP GUIDE)
Let's explore how to create a Dockerfile using docker multistage builds for a simple React application. To create a Docker multistage build, use the following steps:
STEP 1: CREATE A REACT APPLICATION
First, open the vscode and create a new React application if you still need to create one. You can create a React application using the below commands:
> npx create-react-app testapp
> cd testapp
STEP 2: CREATE THE DOCKERFILE FOR
In the root of your React application, create a Dockerfile. In the docker file, paste the following code:
# Use node:16-alpine image as a parent image
FROM node:16-alpine AS build
# Create app directory
WORKDIR /usr/src/app
# Copy package.json files to the working directory
COPY package*.json ./
# Install app dependencies
RUN npm install
# Copy the source files
COPY . .
# Build the React app for production
RUN npm run build
# Use nginx image as a parent image for serving the app
FROM nginx:alpine
# Copy built files from the previous stage to the nginx default directory
COPY --from=build /usr/src/app/build /usr/share/nginx/html
# Expose port 80 for serving the app
EXPOSE 80
# Command to start nginx
CMD ["nginx", "-g", "daemon off;"]
The Dockerfile uses a docker multistage build process. In the initial stage, the React application is built, while the subsequent stage serves the built application utilizing Nginx. Within the second stage, the COPY command transfers the contents of the build directory from the first stage, identified as "build," into the default directory of the Nginx web server. This configuration configures Nginx to host your React application.
STEP 3: BUILD AND RUN THE DOCKER IMAGE
Build your Docker image using the docker build command in the following way:
> docker build -t testapp
STEP 4: CHECKING THE IMAGE SIZE
To assess the impact of the Docker multistage build on the image size, you can list your Docker images once again:
> docker images
The above command will display a list of all Docker images on your system, allowing you to compare the sizes before and after implementing the Docker multistage build process.
Once the build is complete, run a container from the image:
> docker run -d -p 80:80 testapp
You can now access your React application in your browser at http://localhost.
By using docker multistage builds, we've created a Docker image that only contains the necessary files to serve the React application, reducing its size and improving security.
WHAT CHALLENGES MAY ARISE WITH DOCKER MULTISTAGE BUILDS?
Multistage builds, while beneficial, can present certain challenges:
- Build Speed: Due to multiple stages in the Dockerfile, the build process can be slow. Creating a production-ready image involves several steps, which can increase the time required for the build.
- Caching: If you are using the latest Docker version with BuildKit enabled, caching can help improve the build speed. However, this doesn't eliminate the issue, and builds can still be time-consuming.
- Readability: Another challenge is the complexity and readability of the Dockerfile. As more stages are added, the Dockerfile can become harder to understand and maintain, especially for those new to the project.
By being aware of these issues, you can better manage and optimize your use of Docker multistage builds.
WHAT ARE THE BEST PRACTICES FOR CREATING DOCKER MULTISTAGE BUILDS?
Here are some important practices that you should remember while using Docker multistage builds:
Minimize Dependencies in Stages: Ensure that only essential dependencies and files are included in each stage of the build process. This helps reduce the size of your final Docker image and improves overall performance.
Choose Optimal Base Images: Select base or parent images that contain only the necessary packages for your application. Using lightweight base images, such as Alpine Linux variants, can further reduce image size and resource consumption.
Separate Application Data: Avoid including application data directly within the Docker image, as this can inflate its size. Instead, utilize Docker volumes to manage and persist application data separately from the container itself. This approach not only reduces image size but also enhances flexibility and scalability.
By following the above best practices, you can optimize the efficiency and performance of your Docker multistage builds, resulting in smaller, more streamlined container images.
CONCLUSION
Creating Docker images the right way is important because it makes your application faster and more secure. Bigger images can have more security problems, so it's essential to take your time and be careful. Multistage builds have made the process easier by simplifying the steps you need to follow. Docker Multistage builds are a powerful feature that allows you to use in dockerfile multiple from statements that can help you create multiple stages. By separating the build and runtime stages, you can optimize your Dockerfiles and ensure that only the essential components are included in the final image. Give it a try with your applications and see the difference it makes!
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