minimize docker image size

deployment/Dockerfile

@@ -1,5 +1,5 @@
 # build-env ###################################################
-FROM golang:1.15.4 AS build-env
+FROM golang:1.15.5-buster AS build-env
 WORKDIR /app
 
 RUN apt-get update
@@ -17,14 +17,13 @@ ARG SOURCE_COMMIT
 
 COPY cmd cmd
 COPY pkg pkg
-RUN go install -ldflags="-X main.gitRef=${SOURCE_BRANCH} -X main.gitHash=${SOURCE_COMMIT}" ./cmd/wedding
+RUN CGO_ENABLED=0 \
+    GOOS=linux \
+    go install -ldflags="-X main.gitRef=${SOURCE_BRANCH} -X main.gitHash=${SOURCE_COMMIT}" -installsuffix cgo ./cmd/wedding
 
 ###############################################################
-FROM debian:buster
-
-RUN apt-get update && apt-get install -y \
-    ca-certificates \
- && rm -rf /var/lib/apt/lists/*
-
-COPY --from=build-env /go/bin/wedding /usr/local/bin/wedding
-ENTRYPOINT [ "wedding", "server" ]
+FROM alpine:3.12.1
+RUN apk --no-cache add ca-certificates
+WORKDIR /root/
+COPY --from=build-env /go/bin/wedding .
+ENTRYPOINT [ "./wedding", "server" ]