Multistage builds in Docker provide a powerful mechanism for streamlining the creation of Docker images, resulting in smaller, more efficient images for production. The concept involves using multiple FROM statements in a Dockerfile to define distinct stages in the build process. Each stage serves a specific purpose, allowing you to discard unnecessary files and dependencies from the final image. This approach is particularly useful in languages or frameworks where build tools and dependencies are necessary during the compilation phase but not required for runtime.

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Let's delve into an example Dockerfile to illustrate the concept:

# Build Stage
FROM golang:1.16 AS builder
WORKDIR /app
COPY . .
RUN go build -o myapp

# Final Stage
FROM alpine:latest
WORKDIR /app
COPY --from=builder /app/myapp .
CMD ["./myapp"]

Explanation:

• Build Stage (golang:1.16 AS builder):

  • This stage is responsible for building the application.

  • It utilizes a full-fledged Golang image (golang:1.16) to compile the code.

  • The resulting binary (myapp) is copied to the next stage.

• Final Stage (alpine:latest):

  • This stage starts with a minimal Alpine Linux image, which is significantly smaller than the Golang image.

  • It only copies the compiled binary (myapp) from the previous stage, discarding unnecessary build tools and dependencies.

  • The final image is much smaller, containing only the essential components needed to run the application.

By employing multistage builds, you achieve a more optimized and lightweight production image. It reduces the attack surface, improves security, and enhances efficiency by excluding unnecessary components from the final container. This approach is especially valuable in scenarios where you want to keep your containers lean and focused on runtime essentials.