Dockerfile for Go modules and built cache efficiency

README.MD

Also works across git branches if you keep the intermediate build images around, e.g. those <none> images in the docker images output.

FROM golang:1.12 AS builder

# enable Go modules support
ENV GO111MODULE=on

WORKDIR $GOPATH/src/github.com/myrepo/myapp

# manage dependencies
COPY go.mod .
COPY go.sum .
RUN go mod download

# Copy src code from the host and compile it
COPY cmd cmd
COPY pkg pkg
RUN CGO_ENABLED=0 GOOS=linux go build -a -o /myapp cmd/main.go

FROM alpine:3.9
RUN apk --no-cache add ca-certificates
COPY --from=builder /myapp /bin
CMD ["/bin/myapp"]

May I suggest this for security's sake:

# Don't run production as root
RUN addgroup --system --gid 1001 gogroup
RUN adduser --system --uid 1001 gouser
USER gouser

COPY --chown=gouser:gogroup --from=builder /myapp /bin