Docker-compose api and database configuration

Question

I have a problem with connecting Api with MySQL database running in containers. I have Dockerfile for Golang Api:

FROM golang:latest
 WORKDIR /app
 COPY go.mod go.sum ./
RUN go mod download
 COPY . .
WORKDIR /app/bin
 EXPOSE 8080
 RUN go run ./../cmd/web/

I usually connect with database in the application using database/sql:

dsn = "user1:pass@tcp(wpmysql:3306)/wp?parseTime=true"
db, err := sql.Open("mysql", dsn)

My docker-compose.yml:

version: '3'
services:
  db:
    image: mysql:5.7
    container_name: ${MYSQL_CONTAINER_NAME}
    ports: 
        - 3306:3306
    command: --init-file /usr/src/app/init.sql
    volumes:
        - ./init.sql:/usr/src/app/init.sql
    environment:
        - MYSQL_USER=${MYSQL_USER}
        - MYSQL_PASSWORD=${MYSQL_PASS}
        - MYSQL_DATABASE=${MYSQL_DB}
        - MYSQL_ROOT_PASSWORD=${DB_PASSWORD}
    networks:
        - fullstack
  web:
    container_name: wpapi
    build: .
    ports:
        - 8080:8080
    restart: on-failure
    volumes:
        - .:/usr/src/app/
    depends_on:
        - db
    networks:
        - fullstack

networks:
    fullstack:
        driver: bridge

In the same directory as docker-compose.yml is file .env:

DB_PASSWORD=pass
MYSQL_PORT=3306
MYSQL_USER=user1
MYSQL_PASS=pass
MYSQL_DB=wp
MYSQL_CONTAINER_NAME=wpmysql

After call commends:

$ docker-compose up -d db
$ docker-compose build web

I get error ERROR main.go:46: dial tcp: lookup wpmysql on 37.8.214.2:53: no such host. List of containers looks like:

CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                               NAMES
9fbaf67df5bf        2778fcda2046        "/bin/sh -c 'go run …"   14 seconds ago      Up 13 seconds       8080/tcp                            mystifying_shannon
7f6c76cc9c4f        mysql:5.7           "docker-entrypoint.s…"   40 minutes ago      Up About a minute   0.0.0.0:3306->3306/tcp, 33060/tcp   wpmysql

Moreover when I try to connect in application by dsn = "user1:pass@tcp(localhost:3306)/wp?parseTime=true" or dsn = "root:pass@tcp(localhost:3306)/wp?parseTime=true" I get another error: dial tcp 127.0.0.1:3306: connect: connection refused although I can go into container (docker exec -it wpmysql bash -l) and sign in with root and user1 credentials

Answer 1

In your docker file you have:

RUN go run ./../cmd/web/

This will attempt to build AND run your executable during the build process. The network fullstack is not available at this time. I think you probably meant to use:

CMD go run ../cmd/web/

This will set the default command run when you start (i.e. docker-compose up) the container to go run ../cmd/web/. Even better would be:

RUN go build ../cmd/web/
CMD ../cmd/web/web

This will build your application as part of the process of building the container and then set the executable produced as the default command. The benefit of doing this is that compile errors become apparent when you build the image (and it means the application is not built every time you start the container).