License Management for the Virtual Data Center

Although server virtualization has eased the job of network administrators in many ways, it has complicated the task of software license tracking. Traditional per-server or per-processor licensing models simply don't translate well to virtual server environments. What's more, the highly dynamic nature of virtual server lifecycle management can render a licensing report inaccurate shortly after it's created.

There are several steps IT managers can take to make license management of virtualized software more practical:

1. Stick to the spirit of legacy licensing policies.

When working within the confines of legacy licensing policies in a virtual data center, try to adhere to the spirit of the licensing policy. For example, if a product is licensed per server, then treat your virtual servers as if they were physical machines. A product that is licensed for use on a single server should not be run on multiple virtual machines, even if those VMs reside on the same physical host.

License compliance can take on an additional measure of complexity for products that are licensed per socket or per CPU core. The only way to truly comply with a per-socket licensing requirement is to license the product based on the number of CPU sockets present in the physical host. However, an organization could make an exception to this licensing method while continuing to follow the policy in good faith if it uses a hypervisor that supports true CPU affinity. In that situation, the product should only be licensed for the number of sockets that have been allocated to the VM.

2. Use virtualization-aware asset management tools.

Some software makers have begun adapting their licensing policies to make it easier to use their products in a virtual environment, but such policies may not always mesh well with license metering software. For example, a Windows Server 2008 R2 Datacenter Edition license allows for the creation of an unlimited number of Windows Servers on a single virtualization host. Unless license metering software is virtualization-aware, it would most likely report that the VMs running the OS are out of compliance.

3. Include a metering agent in VM templates.

The dynamic nature of VM lifecycle management exacerbates the challenge of license metering in virtual environments. Fortunately, organizations that create a large number of VMs almost always do so from templates. One trick for ensuring that your license usage remains in compliance is to include a license metering agent in your VM templates. That way, each new virtual server will automatically check in with your organization's license metering software.

4. Plan for dynamic VM usage.

Becuase VMs tend to be dynamically created on an as-needed basis and are often temporary in nature, it is useful to take the overall VM lifecycle into account when planning for license compliance.

Purchase site licenses for software whenever possible. Doing so frees the organization from the burden of tracking individual license use.

For applications that don't include virtualization-specific licensing policies and for which purchasing a site license is impractical, implement quotas to prevent license violations. For example, many organizations use a service portal to automatically generate VMs based on template images. Some of these portals contain a quota feature that can be used to limit the number of VMs that can be generated from a template.

While ensuring software licensing compliance in virtual environments can be difficult, this challenge isn't insurmountable. An ever-increasing number of software makers now license their wares for virtual environments.