Hi NICU,
Thanks for your question in Microsoft QnA!
You can use Azure Application Gateway when you need to:
- Route traffic to different backends based on the URL path or hostname.
- Modify the URL of incoming requests before routing them to the backend.
- Protect your applications from common web attacks with a WAF.
- Load balance traffic within a specific region or virtual network.
You can use Azure Front Door when you need to:
- Distribute traffic across multiple regions and edge locations for optimal performance.(Most Common reason)
- Cache static content at edge locations to reduce latency and improve performance.
- Monitor the health of your backends and automatically route traffic to healthy backends.
- Protect your applications from common web attacks with threat protection.
In general, you can use both Azure Application Gateway and Azure Front Door together to implement a multi-layered load balancing solution. Azure Front Door can be used to distribute traffic globally, and then Azure Application Gateway can be used to load balance traffic within each region.
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