Understanding Cassatt Active Response Virtualization Manager
Intended for use with Cassatt Active Response Premium Edition and Data Center Edition V5.2.
Cassatt Active Response manages virtual machines (VMs) in much the same way it manages physical application nodes: all the same service level agreements and business policies apply. There are some differences, however, in how you add and allocate VMs as virtual application nodes, and there are a few things you need to know about failure. In this article I'll give you an overview of these differences and I'll provide links to the procedures for each activity.
Need some background? Read Cassatt Active Response Basic Concepts: Premium Edition, Data Center Edition. If you just need a quick reminder about the Cassatt Active Response environment's shared infrastructure and how application nodes are allocated to tiers, see the next illustration. I'll use this same paradigm in the graphics throughout this article.
Adding virtual application nodes
Adding virtual application nodes to your Cassatt Active Response environment follows a different process than adding physical application nodes. Instead of cabling hardware, you create a software image that runs your VM Manager (VMM) software, such as VMware or Xen. The image contains your desired number of VM instances (how the VM instances are created depends on which VMM software you are using). For a refresher on software images and Cassatt Active Response, read Understanding Image Creation and Capture.
Next you create a tier that runs the image. Let's call that tier the VM host tier. Tiers run business applications: the VM host tier runs your VMM software. As it does with any other tier, Cassatt Active Response allocates your target number of physical application nodes to the VM host tier. For example, if your target is 3, Cassatt Active Response allocates 3 physical application nodes.
Here's the interesting part: when you activate the VM host tier, each physical application node generates a virtual application node for each VM you specified in your VMM image. So, if your image is configured for 6 VMs, each physical application node generates 6 virtual application nodes.
The resulting virtual application nodes (the tier's target physical application nodes times the number of VMs configured in the image) go through discovery and inventory, and are then made available in the free pool:
target physical application nodes x VMs = virtual application nodes
Example:
If you set target application nodes to 3, and you have configured 6 VMs in the host VM image, Cassatt Active Response allocates 3 physical application nodes into the VM host tier and generates 6 virtual application nodes on each physical application node, for a total of 18 virtual application nodes. The virtual application nodes, though running on the physical application nodes in the VM host tier, are listed in the free pool for allocation to tiers, as shown in the next illustration. |
The VM host tier's only job is to run the VMM to support virtual application nodes, which in turn run your business applications: the virtual application nodes technically are running within the VMM software on the physical application nodes in the VM host tier, but Cassatt Active Response lists them in the free pool for allocation—just like physical application nodes. And when Cassatt Active Response allocates virtual application nodes to a tier, Cassatt Active Response lists them in the appropriate application tiers—again, just like physical application nodes.
A word about VMs and inventory
It may seem nonsensical to say that virtual application nodes go through inventory since VMs don't have real, physical assets. When I say that virtual application nodes go through inventory, I mean they do so virtually. Instead of booting a physical application node and checking physical assets, Cassatt Active Response collects resource information from each VM's definition file on the host application node.
If you change a VM definition file, you can reinventory the virtual application node to update Cassatt Active Response with the revised resources for the node. |
For detailed instructions, use one of these procedures:
Deploying applications to run in virtual application nodes
As I hinted in the last section, to deploy an application that runs in a virtual application node, you need to create an image for the application and assign it to a tier. Let's call that the VM guest image and the VM guest tier. How you create the VM image depends on whether your application is Linux or Windows, and which VMM you are running.
Creating a VM guest tier is no different from creating a tier that uses physical application nodes: you select the Windows or Linux image and set all other tier parameters according to your site requirements.
When you allocate the tier, Cassatt Active Response selects the target number of virtual application nodes from the free pool and allocates the virtual application nodes to the tier—just as if they were physical application nodes.
Last, you activate the tier as usual.
For file-based VM guest images (like Windows with VMware and VBD files with XenEnterprise), Cassatt Active Response copies the virtual disk file onto the local hard drive of the physical application node that hosts the VM (or onto SAN if you have configured the tier for SAN). NFS-based images are PXE-booted onto virtual application nodes just as if they were physical application nodes.
The next illustration shows a business application, represented by the pie chart, deployed in a VM guest tier. Cassatt Active Response has allocated four virtual application nodes from the free pool to the VM guest tier.
Handling a failure
Cassatt Active Response treats failed applications running on virtual application nodes the same way as failed applications on physical application nodes, as long as the underlying host application node remains healthy: if an application running on a virtual application node fails, Cassatt Active Response detects the failure as usual via monitoring (read about Cassatt Active Response monitoring options). If the tier is set to reboot application nodes on failure (recommended), Cassatt Active Response reboots the virtual application node. The application should start normally. If the application does not start, Cassatt Active Response starts it on a replacement virtual application node, and moves the failed virtual application node to the maintenance pool or marks the virtual application node as failed (depending on your automation settings).
If a physical application node hosting VMs fails—taking down the virtual application nodes it hosts—Cassatt Active Response replaces the physical application node as usual. At the same time, Cassatt Active Response deletes all of the virtual application nodes that the physical application node is hosting, whether they are in a pool or allocated to a tier. That's because a virtual application node cannot continue to function without its physical host. For details, see the sidebar Understanding host application node/virtual application node dependencies.
Cassatt Active Response doesn't wait for the replacement physical application node to boot before replacing the virtual application nodes allocated to tiers: Cassatt Active Response looks for virtual application nodes in the free pool that meet your application requirements. If spare virtual application nodes are available, Cassatt Active Response starts your application on those virtual application nodes immediately.
Whether a single virtual application node has failed or an entire physical application node, standard priority and harvesting policies apply when insufficient replacements are available (read about service level agreements for tiers, including node harvesting).
Conclusion
Adding, allocating, and managing virtual application nodes isn't any more difficult than working with physical application nodes; you just need to use the right sets of instructions and be aware of the few differences in how virtual application nodes work with Cassatt Active Response.
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