With the release of Exchange 2010 the native clustering feature (Database Availability Group) is a significant improvement over what was available with all previous versions. Be that as it may, there will still be customers that simply don't want to cluster. Typically, not clustering the application would mean no high availability. VMware changed that with the introduction of VMware HA. By simply enabling this feature (which is literally a check box) all virtual machines, regardless of operating system or application, would be provided protection from an ESX host failure. To take it a step further you could enable VM Monitoring to protect against guest OS failures by monitoring VMware Tools running within the virtual machine. Agnostic protection of the guest OS and application is great, but the question that was consistently asked by our customers was "…what if my application fails?" vSphere 4.1 helps answer that.
With vSphere 4.1, we introduced an application programming interface (API) to provide third-party vendors the ability to integrate with VMware HA. The capability to allow application monitoring agents to interact with VMware HA is enabled per vSphere cluster with additional configuration options available per virtual machine. When enabled, this feature allows application monitoring agents to send application heartbeats to VMware HA. In the event of an application-level failure the application monitoring agent can take action to either bring the application back online, or stop the application heartbeat, causing VMware HA to initiate a restart of the virtual machine. Prior to vSphere 4.1, only VMware tools heartbeats could trigger VMware HA restarts.
To take advantage of the new API Symantec has released ApplicationHA. Using ApplicationHA Exchange administrators can provide application monitoring and availability without having to deploy an Exchange 2010 DAG.
ApplicationHA consists of three components:
- ApplicationHA Console provides the interface between the Guest Component and vCenter Server. This component will be installed on a dedicated server (virtual or physical).
- Guest Component is installed in the virtual machine where the application to be protected is running.
- vSphere Client plug-in enables administrators to view the status of a monitored application and make basic configuration changes.
The Symantec Application HA agent for Exchange 2010 can monitor databases and bring them online and offline. In addition to protecting databases, Exchange 2010 services are also monitored. When an agent detects that a database or service has failed that component will be restarted. If the restart fails multiple times (configurable by the administrator) the agent reports the failure to VMware HA. VMware HA can then restart the virtual machine. The following Exchange 2010 services are monitored by the ApplicationHA agent:
- Microsoft Exchange AD Topology Service
- Microsoft Exchange Replication Service
- Microsoft Exchange System Attendant
- Microsoft Exchange Information Store
- Microsoft Exchange Mail Submission
After the installation of the Guest Component in the Exchange 2010 mailbox VM the vSphere client can be used to configure application monitoring. The ApplicationHA Configuration Wizard allows the administrator to select the installed application to protect (one application per VM), and for Exchange 2010, databases to monitor.
With the application configured for monitoring administrators can use the vSphere client to display the status of the application, start and stop the application, re-configure monitoring, and enter maintenance mode.
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The Settings link on the ApplicationHA tab allows the administrator to set additional configuration options.
- App.RestartAttempts – the number of times that ApplicationHA must try to restart an application before declaring it faulted.
- App.ShutdownGraceTime – maximum time in seconds that ApplicationHA will wait for an application to gracefully shutdown before declaring it faulted.
- App.StartStopTimeout – maximum time in seconds that ApplicationHA will wait for an application to start or stop, after which an informational message is displayed stating that the operation is in progress in the background.
Deploying clustering technologies such as Microsoft Clustering Services within virtual machines is a supported configuration. Many customers have chosen not to take this approach for their critical applications due to limitations around using vSphere features such as VMware vMotion, DRS and in some cases HA. Using vSphere 4.1 and Symantec ApplicationHA can provide the needed application awareness in VMware HA while continuing to provide vSphere features in a supported fashion.
For more information about Symantec ApplicationHA including additional application support see the links below.
http://www.symantec.com/business/application-ha
http://sfdoccentral.symantec.com/appha/5.1/windows/pdf/appha_exch_agent.pdf
-alex
Alex Fontana, Technical Solutions Architect
