What is a multistage build and why is it needed?

Multistage 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 compiling or preparing artifacts, 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 intermediate files and build tools are not included in the final image.
• Enhancing security — development tools are absent in the final image.
• Speeding up build and deployment due to smaller data volume.

Example Dockerfile with multistage build for a Go application:

# 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"]

Thus, multistage build allows creating compact and optimized images without unnecessary dependencies.