Usability testing load balancing

Nginx for two tomcat

1. Under normal circumstances, the request randomly assigned to two tomcat

2. Turn off a tomcat, the request can be processed by still another machine

3. Turn off the recovery machine, the two machines can handle

4. Turn off another machine, requests can still be handled another machine

5. Restored again, the two machines can handle

6. 2 machines are turned off, and then restored to normal processing