Application Availability

Question

If I have a SQL AG on three IaaS servers, two in UK South in different availability zones, and a third in a different region (UK West), what would the uptime be? Would it still be the published 52m36s for a VM or would you take into account the application availability? Thanks

Answer 1

From the Microsoft PoV you don't get an enhanced SLA for deploying a third node. You have this SLA for the two nodes in UK South

For all Virtual Machines that have two or more instances deployed across two or more Availability Zones in the same Azure region, we guarantee you will have Virtual Machine Connectivity to at least one instance at least 99.99% of the time.

https://azure.microsoft.com/en-us/support/legal/sla/virtual-machines/v1_9/

And this

For any Single Instance Virtual Machine using Premium SSD or Ultra Disk for all Operating System Disks and Data Disks, we guarantee you will have Virtual Machine Connectivity of at least 99.9%.

for this third node. And the SLA's are defined in terms of downtime, defined as

"Downtime" is the total accumulated minutes that are part of Maximum Available Minutes that have no Virtual Machine Connectivity in the region.

For

would you take into account the application availability?

Based on these component SLAs, your knowledge of the application architecture and behavior, and your requirements for planned application downtime, you should calculate an expected uptime SLA for the application. Then communicate that (or something less) to the application stakeholders.