Redundant MySql Configuration
What you are looking for is in fact possible. What you are looking to do (like many businesses) is build an automatic failover which is often called a hot standby. A hot standby is just a backup slave server that can be switched to either automatically or manually when you need to do maintenance or if your master server fails.

MySQL has some great documentation on setting that up here 

You may also need to take a look at replication methods for replicating your data to the slave.