What is the best way to use existing external MySQL to Dockerized app?

Question

In company we migrating some applications to Docker Container but apps has been connected to MySQL databse.

task which I stuck is the application is running on Docker and also the MySQL database which used by app I dockerized from officle image. But problem is the database is empty. i need to connect to already existing DB which is seperate server or migrate Data to newly created conternized Image. So I don't know which is best way and how to connect already exisitng db to dockerized app

I wanna ask what is the best way?

a) Dockerize MySQL from official image and migrate all data from host.(but data is very big to migrate) b) Connect App to the already existing database which is outside Docker container. c) Or any other way?

I tried to connect database which is outside Docker but not successfully

docker run -d --network=host \
  -e "DB_DBNAME=database-1" \
  -e "DB_PORT=3306" \
  -e "DB_USER=admin" \
  -e "MYSQL_ROOT_PASSWORD=pass" \
  -e "DB_PASS=4815162342" \
  -e "DB_HOST=database-1.amazonaws.com" \
  --name somemysql2 mysql:latest

Any idea how to connect Docker app to the database which on another server and not in Docker container?

Thanks in advance for your help and support.

Answer 1

You have MySQL running in a Docker Container on a Host.

Different scenario's to connect to that MySQL Database:

From an App in another Container started in the same docker-compose.yml

If you started an App in the same docker-compose.yml and want to connect to the MySQL Database:

Use the Service as the Hostname because docker-compose has its own network and will translate the servicename to to right container

version: '3.9'

services:

  mydb:
    image: mysql:latest
    volumes:
      - "./.mysql-data/db:/var/lib/mysql"
    restart: always
    environment:
      MYSQL_DATABASE: mysqldb
      MYSQL_USER: root
      MYSQL_PASSWORD: root
      
  myapp:
    ....

In myapp you connect to MySQL with mysql://mydb:3306/....

No Ports section!! This is because MySQL itself publishes port 3306, so no Ports section needed in docker-compose.

From an App in another Container started in another Docker command

Suppose your App is started on the same Host but in another Docker command (or in another docker-compose.yml file)

Then you need to access the database via the Host published port. But there's a problem since you cannot access the host from within a Docker Container. (At least not in a stable way, so I leave out the hacky solutions you see here on StackOverflow)

Just create a (sub)domain and point it to your Host.

And make small change in your docker-compose.yml file: Add a Ports section:

    ports:
      - 3333:3306

The database can be found on mysql://subdomain:3333/.....

From an App running somewhere else on another Host.

This is the same as the previous solution:

• Create subdomain
• Publish the port
• Connect to that subdomain

From Docker Container on Host to MySQL on another Server (not in Docker)

Again, same as before

• Create subdomain
• Publish the port on the Host
• Connect to that subdomain

Solution with the subdomain need a ProxyServer?

In case your host also answers other requests from outside, you might need a ProxyServer (Nginx?) to route the 3333 traffic to port 3306 in the container.

And if you do have that ProxyServer, you don't need the Ports section anymore.

(Link to article I wrote about this ProxyServer solution)

Answer to the question in the Problem Description

You want to connect to a MySQL database running on some AWS host.

That database is already running. It has a host, username, password.

Why are you starting a new Docker Container with MySQL Image?

Only thing you should start is that 'sampleapp' container with software connecting to the external MySQL.

I don't understand why you start a MySQL Container again if you already have an external one running on AWS.