cannot open file using dockerfile golang - docker

Question

I have a file on the root of my project, and I am opening it like this:
file, err := os.Open("file.csv")
When I make go run main.go it works. When I use the dockerfile to run the app it doesn't work:
open fiile.csv: no such file or directory
My dockerfile is like this:
FROM golang:alpine as builder
RUN mkdir /build
ADD . /build/
WORKDIR /build
RUN CGO_ENABLED=0 GOOS=linux go build -a -installsuffix cgo -ldflags '-extldflags "-static"' -o main .
FROM scratch
COPY --from=builder /build/main /app/
WORKDIR /app
CMD ["./main"]
I am not used to dockerfiles so any improv is welcome too!

Answer 1

In the line COPY --from=builder /build/main /app/ you only copy the executable. You do not copy the app directory. Replace that line with COPY --from=builder /build /app/
Below I have included an example of how I would write this Dockerfile. Here are some key changes.
Define WORKDIR before COPY instructions so you do not have write directory names twice. This is helpful because if you want to change your app directory, you only need to change it once (and that means smaller chance of bugs).
Use COPY instead of ADD. The Dockerfile reference indicates that COPY is preferred.
You do not have to use RUN mkdir /build before using a WORKDIR or COPY. Those last two instructions will make the directory if it does not exist already.
FROM golang:alpine as builder
WORKDIR /build
COPY . .
RUN CGO_ENABLED=0 GOOS=linux go build -a -installsuffix cgo -ldflags '-extldflags "-static"' -o main .
FROM scratch
WORKDIR /app
COPY --from=builder /build .
CMD ["./main"]