1. In a cluster computing system that includes a plurality of distinct cluster nodes, each including a set of computing hardware and an operating system, a method for reliable task execution, the method comprising: periodically performing token operations by each of the cluster nodes, wherein each token operation updates an operability metric corresponding to that cluster node, and wherein an effectiveness of the update of the operability metric is indicative of timeliness of task execution by that cluster node; in response to completion of the token operation, updating, by each of the cluster nodes, a database containing operability metrics for a plurality of cluster nodes to include each updated operability metric in the database; comparing, by each of the cluster nodes, at least some of the updated operability metrics stored in the database against a benchmark value, wherein the benchmark value is determined from operability metrics stored in the database; in response to the comparing, generating an operability determination, by each of the cluster nodes, as to whether one or more other cluster node is inoperative for carrying out tasks; in response to the operability determination being indicative of the one or more other cluster nodes being inoperative, selecting, by a first one of the cluster nodes, at least one task assigned to the one or more inoperative cluster node; and executing the at least one task by the first one of the cluster nodes in lieu of the one or more inoperative cluster nodes.