With Docker 1.17 the long awaited multi stage builds are now available. It allows you to run several stages in your Dockerfile while reducing the size of the final container.

It is typically used for compiled languages like C, Java or Go, where you need a compiler environment to compile the code, but don’t need it for runtime.

The Dockerfile below is an example showing this in action for a Go application, a single docker build . will:

1. First compile the source code with golang:alpine container (~250MB)
2. Copy the compiled artefact into a scratch container

The resulting runtime image is only 1.86MB (!) and should be the absolute minimum to run the application.

app.go

package main

import (
        "fmt"
)

func main() {
        fmt.Println("Hello Docker")
}

Dockerfile

# compiler container
FROM golang:alpine as build
ENV CGO_ENABLED=1
ADD . .
RUN go build -o /main

# runtime container
FROM scratch
COPY --from=build /main /main
ENTRYPOINT ["/main"]

You can find this example in GitHub RootPi314/docker-examples/go-multistage

This can be easily adapted to cover any compiled language, more info available in the Docker documentation

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