round-robin DNS setups and/or use of haproxy are some of the most common approaches in your scenario (limited budget, early growth phases of site). Round-robin

round-robin DNS setups and/or use of haproxy are some of the most common approaches in your scenario (limited budget, early growth phases of site). Round-robin DNS is basically free to implement, and while it doesn't give you 100% uptime, it helps ensure that a problem on any 1 server only affects a small portion of your userbase.