This section covers the resolution of applications hosted in Azure VNets from on-premises.



FQDN Address Resolution

  1. The client that is present on-prem wants to access Application A. The client sends an HTTPS request to download the home page of Application A. Its FQDN (A.gslb.azure.com) needs to be mapped to an IP address that is not yet known to the client.

  2. As the DNS server configured for this subdomain on corporate DNS is DNS Forwarder IP, the request will go to DNS Forwarder VM for resolution. It will in turn forward the request to the DNS of the Avi Load Balancer (one of the two GSLB DNS instances, in this case to DNS VS1), and eventually, the IP for A.azure.com will be returned to the client.

Application Traffic Flows to Optimal Virtual Service

DNS VS1 has two candidates for the optimal virtual service choice: VS1 A, VS2 A. It chooses VS1 A based on the load balancing algorithm, health, client location, and so on. DNS VS1 responds to the DNS query with the VIP of VS1 A, which eventually makes it to the original client. The client uses the VIP of VS1 A to send its HTTP request.

Local Load Balancing

SEs receive the request that has been directed to the VIP of VS1 A. The request is load-balanced to one of the two servers of VS1 A. VS1 A responds directly to the client.