Symptoms:

• When an ESXi host wakes up from the standby state, the pre-configured Host connection and power state alarm triggers configured actions such as Send a notification email or Send a notification trap, stating that the connection status of the host changed from Green to Red.
• The ESXi host is fully manageable and appears as connected in the vCenter Server, which indicates that it is a false positive alarm.
• The Alarms tab does not show a triggered Host connection and power state alarm.
• The Events view in the Tasks & Events tab of the ESXi host contains entries similar to:
  
  Note: The most recent entries are shown at the top.
  
  Task: Exited standby mode
  info
  6/20/2012 10:37:06 PM
  
  Alarm 'Host connection and power state': an SNMP trap for entity hostname was sent
  info
  6/20/2012 10:36:50 PM
  
  Alarm 'Host connection and power state' on hostname changed from Red to Green
  info
  6/20/2012 10:36:50 PM
  
  Alarm 'Host connection and power state' on hostname changed from Green to Red
  info
  6/20/2012 10:36:50 PM
  
  Alarm 'Host connection and power state' on hostname triggered an action
  info
  6/20/2012 10:36:50 PM
  
  Task: Exiting standby mode
  info
  6/20/2012 10:31:05 PM
  Exit standby mode hostname

VMware vCenter Server Appliance 5.5.x
VMware vCenter Server 5.1.x
VMware vCenter Server 6.x
VMware vSphere ESXi 6.7
VMware vSphere ESXi 6.5
VMware vSphere ESXi 5.0
VMware vCenter Server 5.5.x
VMware vSphere ESXi 6.0
VMware vCenter Server Appliance 5.0.x
VMware vSphere ESXi 5.5
VMware vCenter Server Appliance 6.5.x
VMware vCenter Server Appliance 5.1.x
VMware vCenter Server Appliance 6.0.x
VMware vCenter Server Appliance 6.7.x
VMware vCenter Server 5.0.x
VMware vSphere ESXi 5.1  

VMware vSphere ESXi 7.x

The two conditions for this alarm, Host Connection State and Host Power State, are checked simultaneously. After the host receives the command to wake up from standby mode, both conditions can become true for a brief time.

When the power state information changes from Standby to Powered on, the host may not respond to the vCenter Server heartbeats for a short period of time. As the transition from one state to the other occurs very quickly (usually in less than second), the alarm status immediately changes back to Green. Therefore the alarm action may trigger, but the alarm does not remain on the Alarms tab.

As Host connection and power state is a state-based alarm, it is not possible to set the condition length to prevent this behavior.

If alarm actions are configured to send a notification email or SNMP trap when the alarm status changes from Yellow to Red, an unreasonable amount of false alarms could be generated in environments where hosts are frequently entering and leaving the standby mode.

False alarms can be identified with a second notification when the alarm status changes back to Green (if the host connection is successfully restored). To revise the first triggered notification (Yellow to Red) by a second notification (Yellow to Green), you must adjust the trigger and frequency of the alarm.

If changing or disabling the alarm actions is not an option for you, use this workaround to quickly identify false positives by adjusting the trigger and frequency of the alarm:
 

1. Navigate to the object where the alarm is defined (the default is the vCenter Server).
2. Click the Alarms tab, then select the Definitions view.
3. Right-click the Host connection and power state alarm and select Edit Settings...
4. Click the Reporting tab and set the Frequency to 0 (zero) minutes. Do not modify the Range value.
5. Click the Actions tab and enable the Yellow to Green trigger for the desired alarm action (usually email or SNMP notifications) by selecting Once from the list.
6. Click OK to save your changes.
7. Note: If using the vCenter HTML5 client, navigate to Configure > More > Alarm Definitions.