What is multi-stage build and why is it needed?

Multi-stage build is a technique in Docker that allows using multiple build stages within a single Dockerfile. The main idea is to split the build process into several steps, where the initial stages involve compilation and artifact preparation, and the final stage creates a minimal image containing only the files necessary for running.

Why is this needed:

• Reducing the size of the final Docker image, as build tools and intermediate files are not included.
• Increasing security, since the final image does not contain unnecessary tools.
• Simplifying maintenance and readability of the Dockerfile, as all stages are described sequentially.

Example for Go:

# Build stage
FROM golang:1.20 AS builder
WORKDIR /app
COPY . .
RUN go build -o myapp

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

Here, the first stage involves building the application, and the second creates a minimal image with only the binary and necessary libraries.