Is MySQL supposed to be installed alone

I often hear people making statements such as "our MySQL server machine failed", which gives me the impression that they dedicate a single machine as their MySQL server (I guess they just install the OS and only MySQL on it). As a developer not a sysadmin, I'm used to MySQL being installed as part of a LAMP stack together with the web server and the PHP.

Can someone explain to me:

• what's the point of installing MySQL on a separate server? sounds like a waste of resources when I can add the entire lamp stack there and additional servers as well.
• if the database is on a separate machine, how do the apps that need to use connect to it?

When your application platform and your database are competing for resources, that's usually the first indication that you're ready for a dedicated database server.

Secondly, high-availability: setting up a database cluster (and usually in turn, a load-balanced Web/application server cluster).

I would also say security plays a large role in the move to separate servers as you can have different policies for network access for each server (for example, a DMZ'ed Web server with a database server on the LAN).

Access to the database server is over the network. i.e. when you're usually specifying "localhost" for your database host, you'd be specifying the host/IP address of your database server. Note: usually you need to modify the configuration of your database server to permit connections/enable listening on an interface other than the loopback interface.

A separate database server is just part of good, scalable design. This does not matter if your traffic is not very high and a single server truly is enough.

But in busier services, isolating the services from each other is a Good Thing. If someone DDoSses your web server and makes it consume all the resources, that does not bully the database server at all. In shared environments more than one web server is probably using the database server, so if the database server contains data for 50 different web sites, then only one web site going down due the DDoS is better than taking everything down.

Also from sysadmin point of view it's more clear if there are dedicated servers named sensibly, such as "mysql-01.yourcompany.com" and "webserver-01.yourcompany.com". When they get alerts, they immediately see what's going on, at least in the sense of "OK, there's something wrong with the database". I know this is a weak argument since several DNS names could point to a single server but still.

Your applications would connect to a remote database server without problems over the network. Aieeeeeee! How does your web browser connect to a remote server? It's magic! Erm.... more seriously, instead of 'localhost' you just provide the server address in $programming_language_of_your_choice and you're all set.