I was talking about consul and etcd.

In the linked consul documentation, we see a `LockIndex` field in the lock state; https://www.consul.io/docs/agent/http/kv.html confirms that "LockIndex is the number of times this key has successfully been acquired in a lock. If the lock is held, the Session key provides the session that owns the lock."

So you can do fencing with consul.

For etcd: https://coreos.com/etcd/docs/0.4.7/etcd-api/

node.modifiedIndex appears sensible for fencing.