MYSQL:Connect to both localhost & host.docker.internal - mysql

Question

I have to connect to both localhost as well as docker.
const db = new Sequelize({
host : 'host.docker.internal'| process.env.DB_HOST,
database: process.env.DB_NAME,
username: process.env.DB_USER,
password: process.env.DB_PASS,
dialect: 'mysql'
})
In the following code , when I run
node app.js it runs on the machine. But when I run docker run -p 3000:3000 [imagehash] it throws the following error
ConnectionRefusedError [SequelizeConnectionRefusedError]: connect ECONNREFUSED 127.0.0.1:3306
and when I run
const db = new Sequelize({
host : 'host.docker.internal',
database: process.env.DB_NAME,
username: process.env.DB_USER,
password: process.env.DB_PASS,
dialect: 'mysql'
})
it runs perfectly on docker run -p 3000:3000 [imagehash]
How to run on both perfectly
NOTE : process.env.DB_HOST = localhost

Answer 1

When you construct the database connection information, check the environment variable first. It's often useful to set the fallback value to what you'd want this to be in your everyday development environment.
const db = new Sequelize({
host: process.env.DB_HOST || 'localhost',
...
});
Then when you do run it in Docker, you need to provide the value of that environment variable.
# If the database isn't in a container
docker run -e DB_HOST=host.docker.internal -p 3000:3000 myapp
# If the database is in a container; typical Compose setup
version: '3.8'
services:
app:
build: .
environment:
- DB_HOST=db # matching the name of the service below
ports:
- 3000:3000
db:
image: mysql
volumes:
mysql_data: /var/lib/mysql/data
volumes:
mysql_data:

Answer 2

I think you try to connect to a mysql db who run on the host,
To make it work just add --network host argument to your run command.
related documentation
After that, the best pratice is to create a mysql db inside container and link it with your application