Node.js able to connect to MySQL container when app is ran locally but unable to connect when app is ran in a container - mysql

Question

Docker-Compose file:
version: '3.8'
networks:
app-tier:
driver: bridge
services:
mysql_node:
image: mysql:5.7
restart: always
environment:
MYSQL_DATABASE: 'sample_db'
MYSQL_USER: 'user'
MYSQL_PASSWORD: 'password'
MYSQL_ROOT_PASSWORD: 'password'
ports:
- '3306:3306'
expose:
- '3306'
volumes:
- mysql_db:/var/lib/mysql
app:
depends_on:
- mysql_node
build: .
ports:
- 3000:3000
environment:
- MYSQL_HOST=mysql_node
- MYSQL_USER=root
- MYSQL_PASSWORD=password
- MYSQL_NAME=sample_db
- MYSQL_PORT=3306
- MYSQL_HOST_IP=mysql_node
networks:
- app-tier
volumes:
- .:/app
volumes:
mysql_db:
docker file:
FROM node:latest
RUN mkdir app
WORKDIR /app
COPY . .
RUN npm install
EXPOSE 3000
CMD ["node", "app.js"]
Sourcecode:
const http = require('http')
var mysql = require('mysql');
const hostname = '0.0.0.0'
const port = 3000
console.log(process.env.MYSQL_HOST_IP)
console.log(process.env.MYSQL_PORT)
var con = mysql.createConnection({
host: "process.env.MYSQL_HOST_IP",
user: "user",
password: "password",
port: 3306
});
con.connect(function(err) {
if (err) throw err;
console.log("Connected!");
});
When I run docker-compose up the MySQL container successfully launches. But the app exits, with error code Error: connect ETIMEDOUT.
When I run the app locally via node app.js I end up getting a successful "Connected!" message output to my console.
I'm able to connect to the database via MySQLWorkbench as well. It's just the app is unable to connect to the db when the app is ran as a container.

Answer 1

You've specified that the app should be on a named network and the database shouldn't. Then the database service goes on the default network and the two containers can't talk to each other.
I'd remove the named network from the app, since it's probably not needed.
app:
depends_on:
- mysql_node
build: .
ports:
- 3000:3000
environment:
- MYSQL_HOST=mysql_node
- MYSQL_USER=root
- MYSQL_PASSWORD=password
- MYSQL_NAME=sample_db
- MYSQL_PORT=3306
- MYSQL_HOST_IP=mysql_node
volumes:
- .:/app