Cloud Application Architectures

Know Your Software Licenses

When I cover the issues people face when moving into the cloud, I always start with licensing because it’s a nontechnical problem that is too easy to overlook. Just because you have licensing that works for you in a traditional data center does not mean you can port those licenses into the cloud.

With many cloud environments in operation today, you pay for resources by the CPU-hour. The cheapest virtual machine in the Amazon Cloud, for example, costs $0.10 for each hour you leave the instance in operation. If it is up for 10 hours and then shut down, you pay just $1.00—even if that is the only use you make of the Amazon cloud for that month.

In a real world, you might have the following operating scenario:

• From midnight to 9 a.m., run your application on two application servers for redundancy’s sake.

• From 9 a.m. to 5 p.m., launch six additional application servers to support business-hour demand.

• For the evening hours through midnight, reduce the system down to four application servers.

Adding all that up, you pay for 110 hours of computing time. If you were using physical servers, you would have to purchase and run eight servers the entire time.

Unfortunately, not all software vendors offer licensing terms that match how you pay for the cloud. Traditional software licenses are often based on the number of CPUs. An organization that uses 10 application servers must pay for 10 application server licenses—even if 5 of them are shut down during the late night hours. ...