High cpu load on only one node

Hi,all
I have a cluster with 21 nodes,es5.3.0(31.9G heapsize).Only one has high cpu load around 90%,and load average about 30 while the others are 10% 5. The nodes are all using ssd data store,and gc well.
Any ideas for this issue?

May be you are sending all your requests to the same node?