Architecting for Scale

Chapter 23. Cloud Resource Allocation

To effectively and efficiently utilize cloud resources, you need to understand how they are allocated, consumed, and charged. Cloud resources can be divided reasonably into these two categories:

• Allocated-capacity resources

• Usage-based resources

Allocated-Capacity Resource Allocation

Allocated-capacity resources are cloud resources that are allocated in discrete units. You specify how much of a specific type of resource you need, and you are given that amount. This amount is allocated to your use, and you are allocated that amount independent of what your real needs are at the moment.

Allocated-capacity cloud resources can be recognized by the following characteristics:

• They are allocated in discrete units.

• You specify how many units you want, and they are allocated for your use.

• If your application uses less of the resource, the allocated resources remain idle and unused.

• If your application needs more of the resource, the application becomes resource starved.

• Proper capacity planning is important to avoid both over and under allocation.

The classic example of allocated capacity cloud resources are servers, such as Amazon EC2 instances. You specify how many instances you want as well as the size of the servers, and the cloud allocates them for your use. Additionally, managed infrastructure components such as cloud databases¹ use an allocated capacity model. In all of these cases, you specify the number of units and their ...