Docker Dev Environment for GO

What I want to do

I want to set up docker dev environment fo Go.

Code

// directory
project(absolute path: /Uses/[username]/project)
|--- app
|  |--- config
|  |  |___ config.go
|  |--- main.go
|  |___ config.ini 
|--- docker-compose.yml
|___ Dockerfile

// main.go
package main

import (
	"app/config"
	"fmt"
)

func main() {
	fmt.Println("Hello World")
	fmt.Println(config.Config.ApiKey)
	fmt.Println(config.Config.ApiSecrete)
}

// docker-compose.yml
version: '3.8'

services:
  app:
    build: .
    tty: true
    volumes:
    - ./app:/go/src/app

// Dockerfile
FROM golang:latest
RUN mkdir /go/src/app
WORKDIR /go/src/app
ENV GO111MODULE=on
ENV GOPATH /go
ADD ./app /go/src/app/

Dev Environment

When I run docker-compose exec app go env, I get

GOPATH="/go"
GOROOT="/usr/local/go"

Problem

When I run docker-compose up -d --build,
I get
package app/config is not in GOROOT (/usr/local/go/src/app/config).
So, I can't import "app/config" in main.go file.

I want to know how import self-made package when I set up GO dev environment with docker.

You can follow the go-env-series about how to use Docker to define your Go development environment in code.
Example: chris-crone/containerized-go-dev

The second article does mention go mod init, which helps with import path:

> Let’s make the current directory the root of a module by using go mod init:
>
> $ go mod init example.com/hello
> go: creating new go.mod: module example.com/hello
>
> The go.mod file only appears in the root of the module.
>
> Packages in subdirectories have import paths consisting of the module path plus the path to the subdirectory.
>
> For example, if we created a subdirectory world, we would not need to (nor want to) run go mod init there.
The package would automatically be recognized as part of the example.com/hello module, with import path example.com/hello/world.

Thanks to you, I've solved this problem, so I'll share.

I run go mod init app, and go mod tidy.

Then, I change Dockerfile to set GO111MODULE=on.

version: '3.8'

services:
  app:
    build: .
    tty: true
    volumes:
    - ./app:/go/src/app
    environment:
      - "GO111MODULE=on"

// directory
project(absolute path: /Uses/[username]/project)
|--- app
|  |--- config
|  |  |___ config.go
|  |--- main.go
|  |--- config.ini 
|  |--- go.mod
|  |___ go.sum  
|--- docker-compose.yml
|___ Dockerfile

cf.
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