Application gateway zone support

Question

I tried creating an app gateway with 3 zones and was able to create it with one instance

This thread suggests that behind the scenes 3 instances are created, but I don't see them in the resource configuration, and it makes me wonder what is the actual configuration and cost here

From reading this article about HA of application gateway service I can understand that the service knows how to handle instances creation. By using availability zone support, it means that instances are created at different zones every time based on some internal logic of the service

Which one of the above theories is the correct behavior?

Answer 1

Hi @Assaf L ,

Welcome to the Microsoft Q&A Platform. Thank you for reaching out & I hope you are doing well.
I understand that you would like to know about the instance manual and autoscaling with respect to Zone-redundant app gateway.

Since we are discussing Zones, I take it that we are considering V2 and V2 WAF Application gateway.
Please correct me if this is wrong.

Now, with V2 and V2 WAF, customers are not charged for instance count, rather for the Capacity units.
This is explained in Understanding Pricing for Azure Application Gateway and Web Application Firewall

Now, to answer your question,
If you are to manually set the instance count to a number X, then you will have only X instances in the backend.

In the example you have mentioned with 3 Zones and 2 Instance,

• You will have only 2 instances.
• We will not have the visibility to know which two Zones these instances spawned.
• However, the internal algorithm makes sure that the instances are evenly distributed across the Zones

I hope this helps.
Please let us know should you have additional queries on this

Thanks,
Kapil

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Answer 2

Here is what I see about HA perspective of Application Gateway deployment. Looks like the reference you forwarded is not saying the same description

Reference: application-gateway-faq

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