Application load balancer issue 404 Not Found/Microsoft-Azure-Application-Gateway/v2

Question

I have configured a vmss as the backend and as the frontend, I have deployed an application Gateway, now when I change the DNS IP address from the old IP to the new application IP then the error gives, I have multiple sites in that one VM which is set an auto-scale mode under vmss.

The architecture will be, vmss(with 1 VM and will autoscale up to 3 VM), and application load balancer, and DNS(not in Azure)

Answer 1

Hello,

Thank you for posting in Q&A forum.

When you try to change the DNS IP address, it may result in errors. This may be related to the TTL (Time to Live) of DNS records. TTL defines the time that DNS records are stored in DNS servers and various levels of cache. If you encounter problems immediately after changing the IP address, this may be due to DNS records still being cached.

Solution

Firstly, you can wait for the TTL to expire. Once the TTL expires, the DNS server will update its cache and start using the new IP address.

If you have access to the DNS server, you can try manually refreshing the DNS cache. This will force the DNS server to immediately update its records and start using new IP addresses.

You mentioned that automatic scaling is set up in VMSS to ensure that new virtual machine instances can also be registered correctly with DNS servers, and the load balancer can correctly route traffic to these instances.

Ensure that the configuration of the application gateway is correct, and it should correctly forward traffic to the new IP address.

These are some possible solutions, but the specific steps may depend on your environment and architecture. If you need more help, please provide more details so that I can better assist you in solving the problem.

Best regards，

Jill Zhou

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