title: consensus algorithm: what will happen if an odd cluster becomes even because of a node failure?
body: <p>Consensus algorithm (e.g. raft) requires the cluster contains an odd number of nodes to avoid the split-brain problem. </p>
  
  <p>Say I have a cluster of 5 nodes, what will happen if only one node fails? The cluster has 4 nodes now, which breaks the odd number rule, will the cluster continue to behave right? </p>
  
  <p>One solution is to drop one more node to make the cluster contain only 3 nodes, but what if the previously failed node comes back? then the cluster has 4 nodes again, and we have to bring the afore-dropped node back in order to keep the cluster odd. </p>
  
  <p>Do implementations of the consensus algorithm handle this problem automatically, or I have to do it in my application code (for example, drop a node)?</p>