如何在monorepo中设置protobuf，grpc和Go模块？

I'm trying to create a microservice-based API in Go, very basic, just to learn some stuff. I have three main goals I have to achieve.

1. Monorepo.
2. Be able to use different back-end languages as need arises (ie. one microservice in Go, two in Node.js, one in Python).
3. Use gRPC.

Currently my structure looks like this (and is stored in ~/Projects/tkg, outside of GOPATH).

Each "service" should be a self-contained application written in a "whatever". As you can see I have a Go service and a React front-end application. Additionally there is a Makefile there that I want to use for building stuff, but I might move to shell scripts, Docker, whatever. Doesn't matter.

So now the question. How can I make generated proto files play well with this setup? I think I don't understand something about Go modules and packages because I cannot set it so articles.go (from cmd) can access the generated api/article.pb.go. How to do it?

// services/articles/go.mod
module tkg/services/articles

go 1.12

require (
    github.com/golang/protobuf v1.3.2
    google.golang.org/grpc v1.22.1
)

// services/articles/cmd/article.go
package main

import (
    pb "tkg/services/articles/api/article"
)

type repository interface {
    Create(*pb.Article) (*pb.Article, error)
}

func main() {

}

// services/articles/api/article.proto
syntax = "proto3";

package article;
option go_package = "tkg/services/articles/api/article";
...

// Makefile
build:
    protoc services/articles/api/article.proto --go_out=.

I have tried various different package names in go.mod, different go_packages in the proto file, I had tried different protoc commands and paths. I bet this is silly and it's very obvious to someone who is well-versed in Go, but for someone from Node.js backgroud like me the inability to do import "../api/article.pb.go" is infuriating. :(

The error I am getting is: could not import tkg/services/articles/api/article (no parsed files for package tkg/services/articles/api/article). Of course with different values for package names. I've been trying to solve it for two days now.

How would you approach this problem?

If you are generating the .pb.go file in the same directory as the .proto file (recommended), then your import path should read:

import (
    pb "tkg/services/articles/api"
)

(not tkg/services/articles/api/article.)

Go packages are collections of .go files in a single directory - each with the same package XYZ first line - where XYZ is the package name. So when importing a package, one uses the package base directory - not including any .go filenames.

Edit: (this was too long to fit into a comment):

I would step back and think about the base-directory of your entire project.

Standard go packages are usually single words like time, sync etc. because they are part of go's standard library. All other packages should have a full internet path. These typically match a git repo address (e.g. "github.com/boltdb/bolt") - but not always e.g. ("gopkg.in/yaml.v2"). This is actually superior to the centrally-hosted NPM package model - as it easily allows for pulling packages from any repo host. Also since repos are cloned to local disk - those same paths can exist on your local disk first (before they've been hosted on the internet, say for development purposes).

So I would suggest naming your local base-directory something like:

github.com/myname/myproj/tkg/services/...

and then ensure you import packages based on this directory structure e.g.

import "github.com/myname/myproj/tkg/services/api"

If a go build does not pick up the generated (.pb.go) code, then there is something up with your GOPATH or if using the new go-modules your go.mod setup.