Page Comparison

• The business scope of Holmes is different from that of Policy

Both Holmes and Policy adopt Drools as the rules engine. The main difference between these two projects is that Holmes is mainly targeted at correlation analysis between different alarms while Policy is aimed to implement control loops by triggering a series of actions. Briefly speaking, Holmes is targeted at root cause analysis but policy is aimed for auto-healing/auto-scaling.

• Holmes is necessary for reducing the pressure caused by the large alarm quantity for Policy
  

Policy does not need to face the original alarms with the help of Holmes. The root cause is picked out from all the original alarms by Holmes and then, the most suitable policy ID is selected and published accordingly. In this way, Policy is liberated from triggering similar or duplicated actions which are caused by the alarms with internal relations.

For example, if there are 3 events A, B and C which could lead to a power down fault, and B and C are caused by A. Without Holmes, all of these 3 events will be sent to Policy and 3 corresponding actions are going to be triggered. After we add Holmes to the close loop controller and make it the upstream system of Policy, only Event A will be sent to Policy and thus only one action will be triggered, which makes the close loop control more precise and efficient.