1. A system comprising: a processor; and a graph component configured to be operated by the processor to generate a dependency graph for a plurality of network components, each network component represented as a node in the dependency graph and each dependency relationship between a pair of network components represented as an edge between two nodes; a diagnostic component configured to be operated by the processor to perform operations including: detecting abnormal behavior of a first network component of the plurality of network components based on behavior metrics of the first network component and historical values of those behavior metrics; for each pair of network components of the plurality of network components having a dependency relationship, computing a likelihood that behavior of one network component of the pair is impacting behavior of the other network component of the pair, the computing being based on joint historical behavior of the pair of network components; and determining that a second network component of the plurality of network components is a probable cause of the detected abnormal behavior of the first network component based on the computed likelihoods, wherein magnitudes of the computed likelihoods are directly proportional to magnitudes of differences between behavior metrics and historic values of those behavior metrics for the pairs of network components associated with the computed likelihoods.