When do you move your database to a separate server?

This is more of a conceptual question about when is the appropriate time to spit a database server off to it’s own droplet.

So say you have a LAMP type solution running on a 2vcpu/4GB droplet and you think it’s time to get some more capacity. Doubling the size of the droplet is easy, but is that the right way to go? Spinning up a separate database server is another option with some advantages and some disadvantages.

Advantages:

• Isolated database cannot be stopped by overloaded processes on the web/application server.
• The database is further isolated from a security perspective.
• Problem diagnosis and performance monitoring is easier as the web and database loads are separated.
• Simplified maintenance and upgrades because the web application can be pointed at a new/replacement database server that is already tested and operational.

Disadvantages:

• network latency for requests to the database server (same datacenter)
• less overall capacity for a spike in resources needs by the web application processes or the database.

I’m split right down the middle on the advantages vs disadvantages and thought I might find some interesting and informative opinions in the DO community.