Docker Multi State Build

Dockerfile

## https://docs.docker.com/build/building/multi-stage/
## With multi-stage builds, you use multiple FROM statements in your Dockerfile. 
## Each FROM instruction can use a different base, and each of them begins a new stage of the build. 
## You can selectively copy artifacts from one stage to another, leaving behind everything you don't
## want in the final image.

# syntax=docker/dockerfile:1
FROM golang:1.21 as build
WORKDIR /src
COPY <<EOF /src/main.go
package main

import "fmt"

func main() {
  fmt.Println("hello, world")
}
EOF
RUN go build -o /bin/hello ./main.go

FROM scratch
COPY --from=build /bin/hello /bin/hello
CMD ["/bin/hello"]

Stop at a specific build stage https://docs.docker.com/build/building/multi-stage/#stop-at-a-specific-build-stage
When you build your image, you don't necessarily need to build the entire Dockerfile including every stage. You can specify a target build stage. The following command assumes you are using the previous Dockerfile but stops at the stage named build:

docker build --target build -t hello .

Use an external image as a stage https://docs.docker.com/build/building/multi-stage/#use-an-external-image-as-a-stage
When using multi-stage builds, you aren't limited to copying from stages you created earlier in your Dockerfile. You can use the COPY --from instruction to copy from a separate image, either using the local image name, a tag available locally or on a Docker registry, or a tag ID. The Docker client pulls the image if necessary and copies the artifact from there. The syntax is:

COPY --from=nginx:latest /etc/nginx/nginx.conf /nginx.conf