A method for measuring performance of system. The method includes the steps of retrieving a metric definition from a declarative metrics specification, obtaining a list of computing nodes from a database that are currently assigned to the metric definition, obtaining resource data provided by the computing nodes in the list of computing nodes and determining the metric of system performance based on the metric definition and the resource data. The computing nodes in the list of computing nodes are nodes of a cluster of nodes having a dynamically varying node count.