question: @ Nullable private TcpDiscoveryNode resolveCoordinator ( @ Nullable Collection < TcpDiscoveryNode > filter ) { synchronized ( mux ) { Collection < TcpDiscoveryNode > excluded = F . concat ( false , failedNodes . keySet ( ) , leavingNodes ) ; if ( ! F . isEmpty ( filter ) ) excluded = F . concat ( false , excluded , filter ) ; return ring . coordinator ( excluded ) ; } }
target:  Resolves coordinator. Nodes that are leaving or failed (but are still in topology) are removed from search as well as provided filter.