I run two completely independent websites. I am moving their MySQL databases to Amazon RDS.
I'm not going to do Multi A/Z deployment - let's remove that variable from this question.
I'm not sure whether to create a single RDS instance with two databases, or two Amazon RDS instances with a single database. Ignore cost for the sake of this question. I will not hit the 1 TB data limit so let's ignore that. However, it is extremely important that crashing one of the websites doesn't impact the other.
Based on this document - http://docs.amazonwebservices.com/AmazonRDS/latest/UserGuide/Concepts.DBInstance.html
I'm assuming that if I write terrible code that crashes one of the databases in a given RDS instance, it could possibly take down the entire RDS instance (and thus inadvertantly affect the other database). Is that correct?
In response to the comment, we're definitely entertaining the idea of two RDS instances, each with its own database. I just want to make sure that there is actually a benefit to doing that - I'm assuming the benefit is that these databases won't possibly affect each other when they're on separate instances. I thought there was a shot that even on the same instance, they couldn't impact each other, but it sounds like that's not the case.
--EDIT Hop3less - thanks for the answer - however, When I said a two RDS instances with a single database, i meant each having a single database. Just want to make sure you realize I don't mean two EC2 instances. I assume a single RDS instance is still a single point of failure?