Is the DB always connected to the same destination?

It literally returns the hostname of the database you are connected to. Of course, if a DB is in a single server and you have properly specified a destination for that single server's DB, it will be the same.

However, infrastructure configurations can be used to break that assumption.
For example, a read replica can be provided to change the destination of servers connected by DNS round robin or load balancer at complete random.
In that case, which server is randomly connected to?You can get the information that

However, it does not change behavior depending on the server.It's just an environment variable, so you can think of it as a variable for debugging and logging, and it's not often used in simple applications.