How to specify a directory where a Dockerfile is

I’ve recently started learning Docker and Go. While coding, I faced a difficult problem and managed to solve it, so I’m going to summarize it.

Directory Structure

>AppName
  # blah blah
  >docker
    >web
      >Dockerfile
  >docker-compose.yml
  >go.mod
  # blah blah

docker-compose.yml

version: '3'
services:
  web:
    build: ./docker/web
    tty: true
    command: go run .
    volumes:
      - .:/go/src/projects/AppName
    ports:
      - "3000:3000"
    environment:
      MYSQL_HOST: AppName_DB
    networks:
      - AppName_default

Dockerfile

FROM golang:latest

RUN apt-get update && apt-get install -y vim
RUN apt-get update && apt-get install -y locales \ 
  && sed -i -e 's/# \(ja_JP.UTF-8\)/\1/' /etc/locale.gen \
  && locale-gen \
  && update-locale LANG=ja_JP.UTF-8

RUN mkdir /AppName

WORKDIR /AppName

ADD  . /AppName

RUN go get github.com/go-sql-driver/mysql

Problem

And then, I executed like below.

docker-compose up  --build

However, the result was

 > [7/7] RUN go get github.com/go-sql-driver/mysql:
#11 0.255 go: go.mod file not found in current directory or any parent directory.
#11 0.255       'go get' is no longer supported outside a module.
#11 0.255       To build and install a command, use 'go install' with a version,
#11 0.255       like 'go install example.com/cmd@latest'
#11 0.255       For more information, see https://golang.org/doc/go-get-install-deprecation
#11 0.255       or run 'go help get' or 'go help install'.

What did I have to do?

Reason

Dockerfile can’t refer to files in its parent directory, which means if the dockerfile is in the root directory, the bug doesn’t happen.

Answer

I had to fix docker-compose.yml.

version: '3'
services:
  web:
    build: 
      context: .                           #here
      dockerfile: ./docker/web/Dockerfile  #here
    tty: true
    command: go run .
    volumes:
      - .:/go/src/projects/AppName
    ports:
      - "3000:3000"
    environment:
      MYSQL_HOST: AppName_DB
    networks:
      - AppName_default

Dockerfile can be recognized as if it existed in the root directory by writing above.

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