Multi stage docker build of a golang application can't find the .env file

Question

I'm trying to debug a multi-stage docker build for a golang app that is driving me nuts.

The docker file is as follows

FROM golang:1.15-alpine as build

RUN apk add --no-cache git

ENV GO111MODULE=on \
    CGO_ENABLED=0 \
    GOOS=linux \
    GOARCH=amd64


WORKDIR /build

COPY go.mod .
COPY go.sum .
RUN go mod download

COPY . .

RUN go build -o main .

WORKDIR /dist

RUN cp /build/main .
RUN cp /build/.env .

WORKDIR /dist/keys
RUN cp /build/keys/* .

FROM alpine as runtime

COPY --from=build /dist/main /app/
COPY --from=build /build/keys/* /app/keys/
COPY --from=build /build/.env /app/

CMD [ "/app/main" ]

And if I build this and run it with -it /bin/bash and I can see that the app is in the right place, the .env file is there and the keys are also there.

Infact I can interactively run the ./main application happily.

But.. when I try and do

 - docker run -it --rm --hostname dld --name dld dld                               15:57:42
2021/02/17 05:57:47 Error loading .env file

It can't find the .env file obviously.

I was trying to build the second stage from scratch, but I couldn't do anything interactively with that so though I'd try alpine to debug things.

To get the shell I ran

docker run -it --rm --hostname dld --name dld dld /bin/sh

Answer 1

OK found a script that works.

FROM golang:1.15-alpine as build

RUN apk add --no-cache git

ENV GO111MODULE=on \
    CGO_ENABLED=0 \
    GOOS=linux \
    GOARCH=amd64


WORKDIR /build

COPY go.mod go.sum ./
RUN go mod download

COPY . .

RUN go build -o main .

WORKDIR /dist

RUN cp /build/main .
RUN cp /build/.env .

WORKDIR /dist/keys/
RUN cp /build/keys/* .

FROM scratch as runtime

WORKDIR /app/keys/
COPY --from=build /build/keys/* ./

WORKDIR /app

COPY --from=build /dist/main .
COPY --from=build /build/.env .

CMD [ "./main" ]