1. A computer-implemented method comprising: receiving a notification of an event regarding a clustered computing system; based on said notification, identifying a pool of connections to said clustered computing system; wherein said notification is received out-of-band of any connection in said pool of connections; wherein each connection in said pool of connections is a connection to a database session of one or more database sessions; and in response to said event, processing one or more connections from said pool, wherein said processing includes: marking said one or more connections as invalid; and aborting said one or more connections; after receiving said notification of said event, receiving a second notification that identifies a start of a particular service that is hosted on a particular server instance of said clustered computing system; and determining a second number of said one or more connections for allocating across a plurality of active server instances that host said particular service; wherein the method is performed by one or more computers.