Traffic is routed to the backend with priority 2 instead of 1 in Front Door Classic

HouMez 351

Hello,

I have a Front Door Classic with 2 backends (Webapps) that are set with priorities:
Webapp 1: Priority = 1 , Weight = 100;
Webapp 2: Priority = 2 , Weight = 100;

In the access logs, I see traffic on both webapps, but I want 100% of the traffic to be routed to Webapp 1 as long as Webapp 1 is available.

How can I achieve this?

KapilAnanth-MSFT 39,211 Reputation points Microsoft Employee

2024-04-22T09:25:48.51+00:00
@HouMez ,

Welcome to the Microsoft Q&A Platform. Thank you for reaching out & I hope you are doing well.

I understand that you would like to forward 100% of the traffic to Webapp1.

From your configuration,

It appears correct.

All the traffic should arrive at Webapp1 as long as it's up and available.

See : Traffic routing methods to origin - Overall decision flow

As next steps,

Can you make sure the health probes are up?

Because in case of a Complete health probe failure , then Front Door considers all origins unhealthy and routes traffic in a round robin distribution across all of them

You can check this using the AFD metrics by the filter

Can you share the health probe configuration.

Cheers,

Kapil
HouMez 351 Reputation points

2024-04-22T10:17:01.7166667+00:00

@KapilAnanth-MSFT
Thanks for your reply!

The health probe doesn't show 100% at all times. The Webapps are running on two separate Premium tiers (P2v3) on two different regions:

Here is my health probe configuration:
KapilAnanth-MSFT 39,211 Reputation points Microsoft Employee

2024-04-22T10:25:01.5333333+00:00
@HouMez ,

Thanks for the info.

Can you confirm if both the Origins (Webapp1 and Webapp2) are part of a single Origin Group?

Because, If you have multiple origins in your origin group and more than one of them is in enabled state, you can't disable health probes.

But from your screenshot, I can see you have the option to Enable/Disable.

(If you see my screenshot, the option is totally grayed out)

Cheers,

Kapil
HouMez 351 Reputation points

2024-04-22T10:46:15.5433333+00:00

@KapilAnanth-MSFT

I had to disable the Webapp 2 origin in order to re-route the traffic to Webapp 1, that's why you see the option Enable/Disable.
This is what the health probe configuration look now after activating both origins:

Another detail that might help, is that these two Origins are part of two seperate Origin Groups:

Origin Group 1: Webapp 1 with priority 1 and Webapp 2 with priority 2
Origin Group 2: Webapp 2 with priority 1 and Webapp 1 with priority 2

Two separate Routing Rules:
Rule 1: Route traffic to Origin Group 1 for Frontend url A
Rule 2: Route traffic to Origin Group 2 for Frontend url B
KapilAnanth-MSFT 39,211 Reputation points Microsoft Employee

2024-04-23T08:27:52.02+00:00
@HouMez ,

In that case, how are you checking that traffic is not getting distributed as per configuration.- For Frontend URL A, traffic should go to Origin Group 1 (WebApp1)

For Frontend URL B, traffic should go to Origin Group 2 (WebApp2)

Can you share the logs for a specific URL(let's say A) and traffic getting distributed across both the WebApps ?

Cheers,

Kapil
HouMez 351 Reputation points

2024-04-23T08:45:05.9566667+00:00

@KapilAnanth-MSFT

I see it in FrontDoor Access Logs (activated through the Diagnostic Settings of the Front Door):
Table 'AzureDiagnostics', columns 'requestURI_s' (Frontend URL) and 'backendHostname_s' (Backend Webapp).
KapilAnanth-MSFT 39,211 Reputation points Microsoft Employee

2024-04-23T12:46:17.6666667+00:00
@HouMez ,

Can you please share the logs?

You may filter it with any one particular "RouteName" so that we can know the requests for a single "RouteName" are indeed going to different "OriginName"

Cheers,

Kapil
HouMez 351 Reputation points

2024-04-23T15:31:00.39+00:00

@KapilAnanth-MSFT
KapilAnanth-MSFT 39,211 Reputation points Microsoft Employee

2024-04-24T05:08:03.1733333+00:00

@HouMez ,

Thanks for the logs.

To troubleshoot further, we will need a specialized 1:1 session, where a support engineer can have a screen share session to pinpoint the issue.

If you have a support plan you may file a support ticket, else please do let us know, we will try and help you get a one-time free technical support.

Cheers,

Kapil

Accepted answer

KapilAnanth-MSFT 39,211 Reputation points Microsoft Employee

2024-04-29T11:57:11.3866667+00:00
@HouMez ,

Welcome to the Microsoft Q&A Platform. Thank you for reaching out & I hope you are doing well.

I understand that you would like to forward 100% of the traffic to Webapp1.

Your Environment :

Two Origin Groups:

Origin Group 1: Webapp 1 with priority 1 and Webapp 2 with priority 2

Origin Group 2: Webapp 2 with priority 1 and Webapp 1 with priority 2

Two separate Routing Rules:

Rule 1: Route traffic to Origin Group 1 for Frontend url A

Rule 2: Route traffic to Origin Group 2 for Frontend url B

Analysis:

From your configuration,

It appears correct.

All the traffic should arrive at Webapp1 as long as it's up and available.

See : Traffic routing methods to origin - Overall decision flow

Azure Support found that certain POPs marked the origin as unhealthy for a short time.

This resulted in the discrepancy in the routing decision.You may keep the environment in observation for a while and see if the issue reemerges or not.

Kindly let us know if this helps or you need further assistance on this issue.

Thanks,

Kapil

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Traffic is routed to the backend with priority 2 instead of 1 in Front Door Classic

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