build 文件 

    1. FROM golang:1.13-alpine AS build
    2. WORKDIR /go/src/github.com/org/repo
    3. COPY . .
    4. ENV GOPROXY=https://goproxy.cn,direct
    5. RUN go build -o server .
    7. FROM alpine:3.12
    8. EXPOSE 8000
    9. COPY --from=build /go/src/github.com/org/repo/server /server
    10. CMD ["/server"]