Consider:

class Boot {
...
def boot() {
...
if (!DB.jndiJdbcConnAvailable_?) {
DB.defineConnectionManager(DefaultConnectionIdentifier, DBVendor)

LiftRules.unloadHooks.append(() =>
DBVendor.closeAllConnections_!())
}
...

When this code has run, there is an unload hook registered. If later the initialization of the database connection fails, then during shutdown we get an infinite printing of:

20:31:37.775 [Shutdown] INFO net.liftweb.mapper.ProtoDBVendor - Closing all connections

This prevents the container from exiting.