add new Dockerfile with multi-stage build that produces a single binary docker image

.circleci/config.yml

@@ -18,7 +18,7 @@ jobs:
       - checkout
       - docker/build:
           image: pboehm/ddns
-          dockerfile: docker/ddns/Dockerfile
+          dockerfile: Dockerfile
 
   docker-build-and-push:
     executor: docker/docker
@@ -28,7 +28,7 @@ jobs:
       - docker/check
       - docker/build:
           image: pboehm/ddns
-          dockerfile: docker/ddns/Dockerfile
+          dockerfile: Dockerfile
           tag: $CIRCLE_SHA1,latest
       - docker/push:
           image: pboehm/ddns

Dockerfile

@@ -0,0 +1,17 @@
+FROM golang:alpine AS builder
+
+RUN apk add --no-cache git
+
+WORKDIR /go/src/github.com/pboehm/ddns
+COPY . .
+
+RUN GO111MODULE=on go get -d -v ./...
+RUN export CGO_ENABLED=0 && GO111MODULE=on go install -v ./...
+
+ENV GIN_MODE release
+
+FROM scratch
+
+COPY --from=builder /go/bin/ddns /go/bin/ddns
+
+ENTRYPOINT ["/go/bin/ddns"]