main.go: no required module provides package

My Go module, stored in GitHub, successfully compiles locally; however, if I try to do it via docker, even locally in the same folder, I get an error complaining that my local package does not exist, for every local import in a subfolder:

=> ERROR [build 7/7] RUN go build -o myrepo-test .                                                                                                                                                                                                                          0.6s 
------
 > [build 7/7] RUN go build -o myrepo-test .:
#14 0.535 main.go:10:2: no required module provides package github.com/myuser/myrepo-test/common; to add it:
#14 0.535       go get github.com/myuser/myrepo-test/common
#14 0.535 main.go:13:2: no required module provides package github.com/myuser/myrepo-test/scraper/data/process; to add it:
#14 0.535       go get github.com/myuser/myrepo-test/scraper/data/process
(....)

Here is my go.mod:

module github.com/myuser/myrepo-test

go 1.16

And the docker file:

# use alpine due to its small footprint
FROM golang:1.16-buster AS build

WORKDIR /app

# download the required Go dependencies
COPY go.mod ./
COPY go.sum ./
RUN go mod download

COPY *.go ./

# FAIL
RUN go build -o myrepo-test .

##########
# Deploy #
##########

FROM gcr.io/distroless/base-debian10

WORKDIR /

COPY --from=build /myrepo-test /myrepo-test

USER nonroot:nonroot

ENTRYPOINT ["/myrepo-test"]

CMD ["/myrepo-test"]

> #14 0.535 main.go:10:2: no required module provides package github.com/myuser/myrepo-test/common; to add it:<br/>
> #14 0.535 go get github.com/myuser/myrepo-test/common

Above implies you have a package common in your source. But COPY *.go ./ won't add these folders to docker build container, it will just copy go files in current directory into docker build. As go build can't find the package common in your source in container, it will try to download it from github, so the build fails.

Then, the correct solution is as next:

Dockerfile:

FROM golang:1.16-buster AS build

WORKDIR /app

# download the required Go dependencies
COPY go.mod ./
COPY go.sum ./
RUN go mod download
#COPY *.go ./
COPY . ./

RUN ls

RUN go build -o myrepo-test .

Above will add all your sources to container including the package common etc, then build could be ok.

You probably have some other folders, hence copy the entire folders and files for the build stage.

Additionally,
Go is a compiled language. What that means is, it will generate a standalone binary executable. You need to do a multi-stage deployment to take full advantage of that. The previous answers only do the build, if you do that, the Go programming language and its libraries will be part of the Docker image and will push the Docker image size to 400-500 MB. If you do the multi-stage build, this will reduce image size drastically to 15-50 MB. Imagine that!

Here's how you do it!

Stage 1: Build: First stage generates the executable.

Stage 2: Deploy: Second stage copies the executable and any environment variables (can skip).

The Dockerfile may look as follows:

# Build
FROM golang:alpine3.17 AS build
WORKDIR /app

COPY go.mod .
COPY go.sum .
RUN go mod download
COPY . .
RUN go build -o /my-go-app

# Deploy
FROM alpine:latest
WORKDIR /app

COPY .env .
COPY --from=build /my-go-app .

ENTRYPOINT ["/app/my-go-app"]