New to docker here. I followed the instructions here to make a slim & trim container for my Go Project. I do not fully understand what it's doing though, hopefully someone can enlighten me.
Specifically there are two steps to generating this docker container.
docker run --rm -it -v "$GOPATH":/gopath -v "$(pwd)":/app -e "GOPATH=/gopath" -w /app golang:1.8 sh -c 'CGO_ENABLED=0 go build -a --installsuffix cgo --ldflags="-s" -o hello'
docker build -t myDockerImageName .
The DockerFile itself just contains
FROM iron/base WORKDIR /app COPY hello /app/ ENTRYPOINT ["./hello"]
I understand (in a broad sense) that the 1st step is compiling the go program and statically linking the C-dependencies (and doing all this inside an unnamed docker container). The 2nd step just generates the docker image according to the instructions in the DockerFile.
What I don't understand is why the first command starts with
docker run (why does it need to be run inside a docker container? Why are we not just generating the Go binary outside of it, and then copying it in?)
And if it's being run inside a docker container, how is binary generated in the docker container being dropped on my local machine's file system?(e.g. why do I need to copy the binary back into the image - as it seems to be doing on line 3 of the DockerFile?)