Docker can't find dependencies in go.mod file

Question

I'm working in a project with GoLang and Docker and using go.mod to maintain the dependencies. The project works fine when i build without docker, but when i try to build the docker image, this error appears:

internal/server/server.go:8:2: cannot find package "github.com/gorilla/mux" in any of:
        /usr/local/go/src/github.com/gorilla/mux (from $GOROOT)
        /go/src/github.com/gorilla/mux (from $GOPATH)
cmd/root.go:7:2: cannot find package "github.com/spf13/cobra" in any of:
        /usr/local/go/src/github.com/spf13/cobra (from $GOROOT)
        /go/src/github.com/spf13/cobra (from $GOPATH)
make: *** [Makefile:30: build] Error 1

Dockerfile

# Build Stage
FROM lacion/alpine-golang-buildimage:1.9.7 AS build-stage

LABEL app="build-status-hub"
LABEL REPO="https://github.com/MSLacerda/status-hub"

ENV PROJPATH=/go/src/github.com/MSLacerda/status-hub

# Because of https://github.com/docker/docker/issues/14914
ENV PATH=$PATH:$GOROOT/bin:$GOPATH/bin

ADD . /go/src/github.com/MSLacerda/status-hub
WORKDIR /go/src/github.com/MSLacerda/status-hub

RUN make build

The Dockerfile actually has more instructions, but i placed here just only the part when the console shows the error.

The Makefile

build:
    @echo "building ${BIN_NAME} ${VERSION}"
    @echo "GOPATH=${GOPATH}"
    go build -ldflags "-X github.com/MSLacerda/status-hub/version.GitCommit=${GIT_COMMIT}${GIT_DIRTY} -X github.com/MSLacerda/status-hub/version.BuildDate=${BUILD_DATE}" -o bin/${BIN_NAME}

go.mod

module github.com/MSLacerda/status-hub

require (
    github.com/Sirupsen/logrus v1.0.6
    github.com/gorilla/mux v1.7.0
    github.com/spf13/cobra v0.0.3
    github.com/spf13/viper v1.2.0
    golang.org/x/crypto v0.0.0-20190219172222-a4c6cb3142f2 // indirect
)

Answer 1

What is happing?

When you are trying to build the app the required deps are not installed in the docker image

Why it occurs in the docker image and not in my local dev env?

In your local dev env you install/get the required deps running commands like the following example.

$ go get -u github.com/go-swagger/go-swagger/cmd/swagger

But each container/image will be an empty/clean env. You need to tell for the docker container that is required to first install the deps.

Solution

• Use Makefiles to create task/commands for your project. See more over it here

• Create a make file command to install the deps and build the project

Makefile Example

.PHONY: setup
setup: @echo Installing dependencies:
    go get -u github.com/go-swagger/go-swagger/cmd/swagger

.PHONY: build
build: setup
    go build -o $(BINARY) $(APP_FILE)

• Then the command make build need be called to create your image instead of the go build used currently.

• Instead of using the go get commands for each dependency use the go dep manager to do it. Following the example.

Makefile

.PHONY: setup
setup: @echo Installing dependencies:
    dep ensure

See more about it here