Azure Application Gateway Probe Configuration

Question

I am attempting to set up an Azure Application Gateway (with WAF) that points to a pool of 2 IIS servers (IaaS VMs) in the backend pool. These servers host a number of websites and I am trying to figure out the best way to set up probes for the health monitor. Essentially what I want is the AGW to remove only the routing for a particular site when its health goes bad, not the whole server. Typically I have seen a single probe added where the -HostName is just the domain (contoso.com) which my understanding would remove the entire server from the backend pool if the health went bad.

Since there are multiple subdomains (a.contoso.com, b.contoso.com etc), would it be better to have a probe set for each one, as well as a rule and listener for each one that leverages the probe? Or would it be best to just stick with the entire domain for probe, listener and rules and just drop the whole server on updates etc?

Essentially its an IIS box running quite a few APIs that are separated by subdomains rather than a single subdomain with custom routes to each API. For performance I would rather keep all the api's reachable in case just one is being updated and down temporarily or has an issue while the others are not.

Answer 1

You can achieve this with multiple http settings, each with its own probe. For example if you have a.domain.com and b.domain.com running on the same set of backend servers, you would create two http settings and two custom probes. Probe1 would probe on a.domain.com as host name and probe2 with b.domain.com. Your backend pool will be a single backend pool with the two servers. Now you can create two rules and attach the two probes & settings to the rules and point them to the same backend pool. The probe will only mark down a.domain.com or b.domain.com but not the whole VM. Hope that helps.