Database Connection Scaling in AWS ECS: Handling Increased Load in a Containerized Spring Boot Application

I have a user_service application that connects to a MySQL database using the following configuration:

datasource:
  url: jdbc:mysql://localhost:3306/user_serviceDB
  username: root
  password: ****
  driver-class-name: com.mysql.jdbc.Driver
jpa:
  hibernate:
  ddl-auto: update
  show-sql: true

I have containerized this application and deployed it on AWS. When the load increases, AWS ECS automatically spins up new instances of the service by creating new containers. In this scenario, what happens to the database connections? Are new database connections created for each new instance, and do these instances connect to separate database instances, or do they all connect to the same database?

If your database is running in the same container as your app(judging from localhost specified within your config), I believe each new container created during scaling will also spin up a new, separate database instance.

On the other hand, if your database is hosted outside the containers, for example, in AWS RDS or an EC2 instance, all containers can connect to the same database. But in this case, the current URL (localhost) won’t work because localhost points to the container itself, not to an external database.

You’ll need to update the database URL to point to the hostname or endpoint of your database, such as the one provided by AWS RDS.

For production environments, I strongly recommend decoupling the database from the app and hosting it externally. This ensures consistency, scalability and easier management as all containers connect to the same centralized database rather than isolated instances.