Azure APIM Multi Region Load Balancing with FrontDoor and Application Gateway

Question

Hi,

I want to achieve low latency multi region deployment of APIM so that traffic always goes to the closest region.
I want to place my Azure APIM in 3 regions (US , Europe and APAC)
APIM will have single US instance created and deployed to multiple regions using Locations with 1 unit in each region (US, Europe and APAC)
Primary region is US so I will get only 1 gateway url

1. So if anyone calls the US instance gateway url, I assume that APIM will automatically route the traffic to closest region ?
   How APIM achieves this ? if a user makes a call from Europe , so the call will go to US APIM Instance or did APIM internally deploy a load balancer in Europe so that the request never leaves Europe?
2. If I change the architecture to Front Door----APIM instance, then will front door automatically route the request to closest APIM region or do I need to set up additional configurations ?
   Please note that backend pool of Front Door will contain only 1 APIM instance url (primary region)
3. And If I change the architecture to Front Door----App Gateway----APIM, then do I need 3 instances of App gateway (for each region) pointing to 3 instances of APIM in each region (MS docs suggest a way to get these 3 urls for each region, as they are not shown in Azure Portal) ?
   or only 1 instance of App gateway will serve the purpose ? which is doubtful as App gateway only load balances within region.

Scenarios 3 is mentioned to implement virtual network architecture..

Please guide.

Answer 1

@AmitJaiswal-8743 Thank you for reaching out to Microsoft Q&A. For External VNET/Non-networked APIM instance i.e., routing of public HTTP traffic is handled automatically to regional gateways using lowest latency method described (with Traffic Manager). However, for internal VNET mode, users own the routing and responsible to route across multiple regions. Refer docs: Routing and Limitations

For your scenario#3, if you are leveraging internal VNET mode with APIM deployed in three regions, and then, you would need 3 application gateway instances (since App gateway is a regional service), pointing to each regional APIM gateways. You can use Rest API call to get private IP addresses of regional gateways i.e., both primary and additional locations and refer screenshot from the sample below:

AdditionalLocation info:

I understand if it would be great to describe this in docs, I will share the feedback internally with the team. I hope this answers your question and feel free to add if you have any questions. I would be happy to assist you.

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