Use multi-stage build for Docker

Dockerfile

@@ -1,16 +1,23 @@
-FROM alpine
+FROM golang:alpine3.13 AS builder
+LABEL stage=builder
+WORKDIR /workspace
+COPY . .
+RUN CGO_ENABLED=0 go build -o rest-server ./cmd/rest-server
+
+
+FROM alpine:3.13 AS final
+WORKDIR /app
 
 ENV DATA_DIRECTORY /data
 ENV PASSWORD_FILE /data/.htpasswd
+ENV PATH="/app:${PATH}"
 
 RUN apk add --no-cache --update apache2-utils
 
-COPY docker/create_user /usr/bin/
-COPY docker/delete_user /usr/bin/
-COPY docker/entrypoint.sh /entrypoint.sh
-COPY rest-server /usr/bin
+COPY docker/. .
+COPY --from=builder /workspace/rest-server .
 
 VOLUME /data
 EXPOSE 8000
 
-CMD [ "/entrypoint.sh" ]
+CMD [ "./entrypoint.sh" ]