HA Deep Dive – Part 4

In this post we are going to see, VM and application monitoring, which is part of HA feature.

   VM and Application Monitoring acts on a different level from HA. VM/App Monitoring responds to a single virtual machine or application failure as opposed to HA which responds to a host failure. An example of a single virtual machine failure would, for instance, be the infamous “blue screen of death”. In the case of App Monitoring the type of failure that triggers a response is defined by the application developer or administrator. 

   VM Monitoring resets individual virtual machines when needed. VM/App monitoring uses a heartbeat similar to HA. If heartbeats, and, in this case, VMware Tools heartbeats, are not received for a specific (and configurable) amount of time, the virtual machine will be restarted. These heartbeats are monitored by the HA agent and are not sent over a network, but stay local to the host.

   When enabling VM/App Monitoring, the level of sensitivity can be configured. The default setting should fit most situations. Low sensitivity basically means that the number of allowed “missed” heartbeats is higher and the chances of running into a false positive are lower. However, if a failure occurs and the sensitivity level is set to Low, the experienced downtime will be higher. When quick action is required in the event of a failure, “high sensitivity” can be selected. As expected, this is the opposite of “low sensitivity”.

   One of the most useful features as part of VM Monitoring is the fact that it takes screenshots of the virtual machine’s console. The screenshots are taken right before VM Monitoring resets a virtual machine. It is a very useful feature when a virtual machine “freezes” every once in a while for no apparent reason. This screenshot can be used to debug the virtual machine operating system when needed, and is stored in the virtual machine’s working directory as logged in the Events view on the Monitor tab of the virtual machine.

   Application Monitoring is a part of VM Monitoring. Application Monitoring is a feature that partners and / or customers can leverage to increase resiliency, as shown in the screenshot below but from an application point of view rather than from a VM point of view. There is an SDK available to the general public and it is part of the guest SDK.

The Guest SDK is currently primarily used by application developers from partners like Symantec to develop solutions that increase resilience on a different level than VM Monitoring and HA. Although Application Monitoring is relatively new and there are only a few partners currently exploring the capabilities.

Source : Duncan Epping