Let's first look at the key goal of the accessibility suite and the Affinity Group.
Availability: - This is predominantly high availability for your deployment. Azure does this through the Fault and Upgrade domains.
Failure Domain: This is basically a different hardware rack in the same data center. The solution will be deployed in two different hardware racks.
Domain update: Just like domain failure domains, but they support updates, not failures. An update domain is a logical unit for instance separation that determines which instances in a particular service will be updated at a particular point in time.
Affinity Group: To explain this, we need to look into Azure DC. Windows Azure data centers are designed for assembly, you can see rows and rows of containers (something like transport containers) that contain clusters and racks. Each of these Containers has certain services, for example, computing and storage, SQL Azure, service bus, access control service, etc. These containers are distributed through the data center.
When deploying a service using Portal or PowerShell, the service will talk directly to RDFE (Red Dog Front End). RDFE manages DC and nodes. The node cluster is controlled by the Fabric controller. When you specify the Affinity Group, the Fabric controller will put all the necessary deployment elements together. This has several advantages, such as reduced latency (since the required elements are close to each other), Networking.
There are new changes associated with the Network Affinity group, you can refer to them ( https://azure.microsoft.com/en-us/documentation/articles/virtual-networks-migrate-to-regional-vnet/ ).
To ask you a question
You must use accessibility if you want to have a highly accessible system, and also want to have SLAs for computing. Without accessibility, it is established that there will be no SLA for your virtual machines or PaaS instances, in other words, individual VM (IaaS) and PaaS instances will not have SLAs and are prone to downtime due to HW failure and OS updates.
The availability set can also be implemented after deployment. Note that there is a cost associated with the availability set, since you have additional instances running, so they will be debited.
The Affinity group that you must include at the time you create the services. It cannot be updated after creation. Therefore, it is very important to include the Affinity group during creation. There are no additional fees for including the Affinity group.
Share your feedback if the answer answers your question.
Krishna Azure
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