Multi-stage builds are a feature in Docker that allows you to build Docker images in multiple stages, each with its own base image and set of instructions. This can help you create smaller, more efficient Docker images by separating the build-time dependencies from the runtime dependencies.

How Multi-Stage Builds Work

In a multi-stage Docker build, you specify multiple FROM instructions in your Dockerfile. Each FROM instruction can use a different base image and starts a new stage of the build. You can copy artifacts from one stage to another, leaving behind everything you don’t need in the final image.

Here’s a simple example:

# First stage: build the application
FROM golang:1.16 as builder
WORKDIR /app
COPY . .
RUN go build -o myapp

# Second stage: create the runtime image
FROM debian:buster
WORKDIR /root
COPY --from=builder /app/myapp .
CMD ["./myapp"]

In this Dockerfile, the first stage uses the golang:1.16 image to build the application. The second stage uses the debian:buster image to create the runtime image. The built application is copied from the first stage to the second stage, and the final image does not include the Go compiler or any of the source code.

Benefits of Multi-Stage Builds

Multi-stage builds have several benefits:

• Smaller image size: By separating the build-time dependencies from the runtime dependencies, you can reduce the size of your Docker images, which can lead to faster deployment times and lower storage costs.

• Simplified build process: You can use different base images for different stages of the build, which can simplify your build process. For example, you can use a base image with all the necessary build tools to compile your application, and then use a smaller base image for running the application.

• Improved security: By reducing the size of your images and including only what’s necessary for your application to run, you can minimize the attack surface of your Docker containers.

• Optimized performance: Multi-stage builds can lead to improved runtime performance as unnecessary dependencies and files are eliminated from the final image, resulting in faster startup times and reduced resource consumption.

• Facilitates CI/CD pipelines: Multi-stage builds are well-suited for integration into CI/CD pipelines, allowing you to create better automation of the build process and ensuring consistent, reproducible results across environments.

Conclusion

Multi builds are a great feature in Docker for creating the smaller, more efficient, and secure Docker images. When using multi builds, you are on your way to creating better Docker images and optimizing your Docker build process.