go-multi-stage-docker

Example of multi stage docker build for Go programs. Multi stage builds simplify the image building and the genereated images are much smaller in the size. This requires docker >= 17.05.

1. Here is our lovely go program that we want to run in the image:

   package main
   
   import "fmt"
   
   func main() {
       fmt.Println("Hello Multistage Docker builds!")
   }

2. Here is the Dockerfile that you can use:

   # gobase layer
   FROM golang:alpine AS go-base
   ADD . /src
   RUN cd /src && go build -o hello
   
   # final layer
   FROM alpine
   COPY --from=go-base /src/hello /app/
   ENTRYPOINT /app/hello

   Here we create two layers:

   • go-base layer: Includes go runtime. We are mounting src directory in the image and compiling our go package(hello.go) and generating the output binary hello.
   • app layer: Extends the alpine image by copying our binary(/src/hello) from the go-base layer to /app/. It also defines entrypoint for the image as our binary(/app/hello)

3. Lets build our image and name it go-multi-stage-docker :

   $ docker build -f Dockerfile -t go-multi-stage-docker:latest .
   

   You can see the new image would be only few MBs in the size :

   $ docker image ls go-multi-stage-docker
   
   REPOSITORY              TAG                 IMAGE ID            CREATED             SIZE
   go-multi-stage-docker   latest              5f037e697b51        4 minutes ago       5.52MB
   

4. Lets run our app/image

   $ docker run --rm go-multi-stage-docker
   
   Hello Multistage Docker builds!
   

Thats it !