In what cases is multi-stage assembly used?

Multi-stage build is used for:

• Reducing the size of the final image: Intermediate build layers containing tools and dependencies needed for building but not for running the application are removed.
• Enhancing security: The final image contains only the necessary executable files and dependencies, minimizing the attack surface.
• Speeding up the build: Cached layers from previous steps are used, saving time during rebuilds.
• Dependency separation: Intermediate layers can contain independent sets of tools and libraries that do not affect each other.

Example:

# Stage 1: Build the application
FROM golang:1.20 as builder
WORKDIR /app
COPY go.mod go.sum ./
RUN go mod download
COPY . .
RUN CGO_ENABLED=0 go build -o /app/my-app

# Stage 2: Final image
FROM alpine:latest
COPY --from=builder /app/my-app /app/my-app
ENTRYPOINT ["/app/my-app"]