February 11, 2021 at 4:31 pm
trying to come up with an architecture for HA. I was thinking of using our on-prem SQL Server as primary, with Azure as secondaries. IT has mandated that putting everything in Azure is too costly, and we wanted to come up with a geo-replicated solution as our customers are all over the place. Does anyone have any thoughts on this? Bad idea? Any major security or transparency challenges?
February 11, 2021 at 9:26 pm
I think you are confusing HA with business continuity (DR). HA is meant for high-availability and generally utilizes servers within the same DC. If the primary server goes down - the secondary server picks up the processing and there is minimal downtime (usually seconds).
If both primary and secondary systems go down then you move to DR - which would be a server (or servers) in a secondary DC.
Now, if you can guarantee the same performance from either location. That is, the same network bandwidth and latency - then you could build out an HA solution across locations. The network performance is required because *any* solution that requires no data loss will need to be able to replicate data across to the other location with as close to zero latency as possible.
For example - using availability groups would require synchronous commit where transactions are committed on the secondary before they can commit on the primary to insure no data loss. If there is latency it will cause performance issues - or would downgrade to asynchronous which allows data loss.
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February 12, 2021 at 1:20 pm
You can set up Availability Groups and other HA solutions using Azure (or AWS, GCP) as the secondary. I haven't had to do it myself in years & years, so I can't detail the process. However, a quick search online will show you how. However, doing it, you will have to pay for the services on Azure. There's no getting around that.
To do something else, you need to build infrastructure. Multiple data centers in multiple locations wherein you can create your geo-replicated solution. For lots of organizations, that's cost prohibitive (not to mention technically challenging) and why they go with a cloud service solution.
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