1. A method for determining the availability of a cluster of computing devices, the method comprising: identifying a plurality of states comprising a state space of the cluster; determining a state space transition pattern between states in the state space; generating a transition matrix by determining transition rates between states according to the state space transition pattern; and determining availability of the cluster by applying Kolmogorov's equation to the transition matrix to determine a system of equations for calculating state probabilities for states in the cluster.