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I have an application gateway which has a routing rule. The routing from application gateway to the VM is based up FQDN (I use Azure private DNS to internally map the VM IP to the FQDN).

To switch traffic to a different VM (as part of an upgrade pipeline) I update the private dns with the new machines IP.

This results in the backend health failing.

Oddly, manually updating the backend pool, or the routing rule in exactly the same form resolves this issue.

Any ideas whats going on? It feels like its caching the DNS?

iasksillyquestions
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1 Answers1

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There are at least 2 solutions.

  1. Stop/Start application gateway: https://learn.microsoft.com/en-us/cli/azure/network/application-gateway?view=azure-cli-latest
  2. Re-write any of the application gateways config as part of the deployment pipeline

In my case I chose to switch from routing based of FQDN to that the IP address of the VM. This makes use option 2.

iasksillyquestions
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