When you try to deploy a windows azure service, you will be prompted with the below window asking you to choose a region or affinity group for deploying your service. Currently there are 8 sub-regions (If “Anywhere US” is a region then “North Central US” is a sub-region).
And as on today the time and space where we stand “A sub-region” is equal to “A datacenter”. Of course you may at some point have multiple datacenters in a sub-region, but currently that’s not the case.
So what is an affinity group and what is its significance?
When you wish to deploy azure services, if you choose an affinity group it will make azure put an effort to deploy the services as close as possible to each other, which in the current scenario above is one-datacenter or one sub-region. And that’s about it.
The advantage of this is:
- Being closer to each other performance will be better– Communication will be faster when a hosting service depends on a storage service or when one hosting service depends on another hosting service.
- Billing impact– Currently bandwidth consumption will be considered ZERO for communications between two roles within the same datacenter. There will be transaction costs but not the bandwidth costs.