Introduction

Docker multi-stage build is a feature that allows developers to build images with multiple stages, where each stage can produce an intermediate image that can be used by subsequent stages. This feature enables developers to build smaller and more efficient Docker images by eliminating unnecessary build dependencies and reducing the size of the final image. In this blog post, we will discuss the benefits of using Docker multi-stage build and how to implement it using code examples.

Benefits of using Docker multi-stage build:

1. Reduced image size: Multi-stage builds can help to reduce the size of Docker images by allowing developers to use intermediate images that contain only the necessary dependencies and libraries for each stage. This can significantly reduce the overall size of the final image.

2. Faster build times: Docker multi-stage build can help to reduce build times by allowing developers to reuse intermediate images that have already been built. This can reduce the amount of time it takes to build each stage of the image.

3. Simplified build process: Multi-stage builds can help to simplify the build process by eliminating unnecessary build dependencies and reducing the number of steps required to build an image. This can make it easier for developers to create and maintain Docker images.

Implementation

To implement Docker multi-stage build, we need to create a Dockerfile that contains multiple stages, each of which can produce an intermediate image that can be used by subsequent stages. Let's look at an example:

# First stage - Build stage
FROM node:14-alpine as builder
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
RUN npm run build

# Second stage - Production stage
FROM node:14-alpine
WORKDIR /app
COPY --from=builder /app/dist ./dist
COPY package*.json ./
RUN npm install --production
CMD ["npm", "start"]

In the above example, we have two stages. The first stage is a build stage that uses the node:14-alpine image as its base image. We then set the working directory, copy the package*.json files, install the dependencies, copy the entire application code, and build the application.

The second stage is a production stage that also uses the node:14-alpine image as its base image. We set the working directory, copy the package*.json files, install only production dependencies, copy the dist folder (which was generated in the first stage) into the current directory, and set the command to start the application.

Notice the --from=builder option in the COPY command in the second stage. This option tells Docker to copy the dist folder from the intermediate image generated in the first stage.

Conclusion

Docker multi-stage build is a powerful feature that can help to reduce the size of Docker images, speed up build times, and simplify the build process. By using multiple stages, each with its own base image and dependencies, developers can create more efficient and streamlined Docker images. With the example provided in this blog post, you can start implementing multi-stage builds in your Docker projects.