Active-Standby versus Active-Active A Hot Standby data center can be used for application recovery or to relieve the primary data center from a heavy workload. Relieving data center resources from a heavy workload is usually referred to as Active-Active DR mode.
One example of Active/Active DR mode involves an application that is active on a single physical server or VM while the network and compute stack are active in two locations. Some exceptions to this definition are specific software frameworks such as GRID computing, distributed database (i.e. Oracle RAC®) or some cases of server load balancing (SLB). When the resources are spread over multiple locations running in Active-Active mode, some software functions are active in one location and on standby in the other location. Active applications can be located in either site. This approach distributes the workload into several data centers.
It is important to clarify these Active/Active modes by considering the different levels of components, which are all related for the final recovery process:
• The network is running on each site interconnecting all compute, network, and security services; and advertising the local subnets outside each data center. Applications active in the remote data centers are therefore accessible from the traditional routed network without changing or restarting any IP processes.
• Storage is replicated on different locations and can be seen as Active/Active for different software frameworks. However, usually a write command for a specific storage volume is sent to one location at a time while the same data is mirrored to the remote location.
Let’s have a deeper look at the service itself offered by multiple data centers in Active/Active mode. Assuming that we have application A on data center 1 (i.e. Paris) that offers an e-commerce web portal for a specific set of items. The same e-commerce portal offering the same items can also be available and active on a different location (i.e. London), but with a different IP identifier. For the end-user, the service will be unique and the location transparent, but the request can be distributed by the network services based on the proximity criteria established between the end-user and the data center that hosts the same application. So, the same application in this case looks Active/Active, but the software that runs on each compute system is performed autonomously in the front-end tier. They are not related except from a database point of view. Finally the whole session is maintained at the same servers and in the same location until the session is closed.