Checking if a Couchbase node is down

i am working with Couchbase server 2.5.1 and the java client.

the Couchbase auto fail-over happens after 30 seconds and Couchbase can only auto fail-over one node until you reset the fail-over counter. because of this limitations i need to develop my own fail over mechanism. i found all the rest commands the allow me to choose a node and fail-over it. now i need to find a way to identify if a chosen node is down.

has any one faced this problem?
does any one has any suggestions?