Azure Application Gateway zone redundant with instance count set to 1

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Configuring an Azure Application Gateway (v2 standard) with zone redundancy (West Europe (Zone 1, 2, 3)) with instance count set to 1 is allowed. How is this possible?

To my knowledge, you should have at least the instance count set to 3 when you select all 3 zones of your region.

What I assume will be happening, either:

  1. Will it enforce a minimum count of three behind the scenes if you specify an instance count fewer than three like App services?. And will I pay 3x the amount 'behind the scenes' too?

Or:

  1. will it just fallback this single instance to another region in case of a zone disaster?
azure-application-gateway
1 Answers

  • if you set your instance count to 1 and and select all 3 zones of your region it will create 3 instances behind the scene ie one in all 3 zone.

  • Since the platform spreads VMs across three zones and you need to account for at least the failure of one zone but if you specify your instance count more than 3 it will count based on this formula : (zone/zone-1)*workload instance count= Total number of instance will create behind the scene.

If a capacity larger than three is specified and the number of instances is divisible by three, the instances will be spread evenly.Otherwise, instance counts beyond 3*N will get spread across the remaining one or two zones

Let's take an example ,if your typical peak workload requires four instances, you should provision six instances: (3/2 * 4 instances) = 6 instances.

And will I pay 3x the amount 'behind the scenes' too.

It will not cost 3x amount. it will cost based on licence you have choosen for zone redundant. Like Premium v2 or Premium v3

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