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Priority of backend not respected when service is restored

Alex Gagnon 87 Reputation points
2021-09-01T19:38:02.783+00:00

Hi there, we have a frontdoor instance with two application gateway instances in separate regions as the backends. We would like to use the active/failover model of disaster recovery, where the secondary AG instance receives no traffic unless the primary becomes unavailable. We've got the primary with priority 1, weight 50, and the secondary with priority 2, weight 50, and neither FD or AG is using session affinity. Initially it works as expected, and we can shift all traffic to the secondary by manually causing the primary to fail by updating the backend to a non-resolvable host. However when we restore the primary, at that point the traffic seems to be doing a 50/50 split, instead of returning 100% of the traffic to the primary. I've fiddled around with connection draining, but it doesn't seem to change things. Any suggestions?

Azure Front Door
Azure Front Door
An Azure service that provides a cloud content delivery network with threat protection.
608 questions
Azure Application Gateway
Azure Application Gateway
An Azure service that provides a platform-managed, scalable, and highly available application delivery controller as a service.
985 questions
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  1. ChaitanyaNaykodi-MSFT 23,911 Reputation points Microsoft Employee
    2021-09-03T01:37:48.1+00:00

    Hello @Anonymous , Thank you for reaching out and apologies for the delayed response here.

    As per the documentation Azure Front Door routes traffic to backend based on priority given that it is marked as enabled and healthy first. Health probe request determine the health of the backend and can be controlled by Load balancing settings, based on these settings and responses Azure Front Door determines the backend health. Please have a look if these settings are causing the observation above. If this is not what is causing the issue I will suggest that you create a support request for this issue, if you do not have a support plan please let me know.. Thank you!