How to pass .env file to docker image in a Go project? - docker

Question

My Go project heriarchy is this:
The main function:
func main() {
path, _ := os.Getwd()
err := godotenv.Load(filepath.Join(path, ".env"))
if err != nil {
log.Fatal("Error loading .env file")
}
server.Init()
}
Here is my docker file content:
FROM golang:alpine AS build-env
LABEL MAINTAINER "Amit Pal <amit.pal#fynchmobility.com>"
ENV GOPATH /go
WORKDIR /go/src
COPY . /go/src/gothamcity
RUN cd /go/src/gothamcity && go build .
FROM alpine
RUN apk update && apk add ca-certificates && rm -rf /var/cache/apk*
WORKDIR /app
COPY --from=build-env /go/src/gothamcity/gothamcity /app
EXPOSE 8080
ENTRYPOINT [ "./gothamcity" ]
I ran the following command to build and run the docker image:
docker build -t gcr.io/${PROJECT_ID}/gothamcity:v1.0 .
docker run -ti gcr.io/miles-ee458/gothamcity:v1.0
I got the error:
2021/01/28 14:34:46 Error loading .env file
What am I doing wrong here? How can I pass the .env file to docker image and execute it?
Also, isn't COPY . /go/src/gothamcity copy the entire project to docker image?

Answer 1

COPY . /go/src/gothamcity only copies .env to build container. You have to explicitly copy it to your main container like this:
FROM golang:alpine AS build-env
LABEL MAINTAINER "Amit Pal <amit.pal#fynchmobility.com>"
ENV GOPATH /go
WORKDIR /go/src
COPY . /go/src/gothamcity
RUN cd /go/src/gothamcity && go build .
FROM alpine
RUN apk update && apk add ca-certificates && rm -rf /var/cache/apk*
WORKDIR /app
COPY --from=build-env /go/src/gothamcity/gothamcity /app
COPY .env /app
EXPOSE 8080
ENTRYPOINT [ "./gothamcity" ]
Reason is that when you are saying "FROM alpine" this becomes a brand new blank container. That's how multi-stage builds are working.