It’s amazing what the AWS team achieved with RDS in a little over a year since it was introduced. The team added the high-availability feature it calls multi-AZ, or multiavailability zone. And after that, it also added read replicas. With these new features, in addition to the existing scalability features, RDS is growing into a serious RDBMS service. You can easily scale up while minimizing downtime, and also scale out without too much hassle.
If your app gets to the point that you need to start scaling either up or out, it is a good idea to switch to multi-AZ if you don’t run it already. If you have a simple RDS instance, you will degrade your service significantly while scaling, as you can expect to lose the ability to write and/or read. With multi-AZ RDS instances, your service is almost uninterrupted.
Scaling up is so easy it is almost ridiculous. The only drawback is that you have some downtime during the operation. If you don’t have multi-AZ enabled, the downtime of your RDS instance could be several minutes, as you have to wait until a new instance is launched and fully functional. For multi-AZ RDS instances, you will experience some downtime as a failover is initiated after the slave has been scaled up (or down). This failover doesn’t take more than a minute most of the time.
If you initiate a scaling activity via the Console, make sure you enable Apply Immediately if you are in a hurry. If you don’t, scaling will take place ...