A method (400) of maintaining availability of service instances (362) on a distributed system (200) includes executing a pool of primary virtual machine (VM) instances (350P), each primary VM instance executing a corresponding individual service instance and including a rate of unavailability. The method also includes determining a number of secondary VM instances (350S) required to maintain availability of the individual service instances when one or more of the primary VM instances are unavailable based on the number of primary VM instances in the pool of primary VM instances and the rate of unavailability. The method also includes instantiating a pool of secondary VM instances based on the number of secondary VM instances required to maintain availability of the individual service instances.