Azure Front Door Health Probe failing

Question

I have an Azure Front Door Premium. The health probes are failing. I know that the app is working on the back end origin because I can hit it with the Azure App Gateway using a local internal V-net address and the app is responding just fine. However if I use the same URL but route it through the Azure Front Door, I get a page with the text:

Our services aren't available right now

We're working to restore all services as soon as possible. Please check back soon.

Using a browser developer tool, I can see that a 504 is being returned in about 4 seconds. The origin is set for 30 second timeout so I know that the timeout setting is ok. The troubleshooting guide that is referenced by the health probe error page says to look for an Accept-Encoding request header being sent from the client. I did this and I can see that there is an Accept-Encoding Request Header being sent. The troubleshooting guide suggests two options: 1. Disable compression on the origin or on Front Door (but it does not tell you how to do that) or 2. Create a rule set to remove the Accept-Encoding Request Header and it gives a rule set example.

I opted for the second option to create a rule set to delete the Accept-Encoding Request Header.

I have done this and associated it with the Front Door endpoint however I am still seeing the Accept-Encoding request header when I make an attempt to reach the endpoint with my browser.

Answer 1

Hi @JohnSebastian-3934,

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

We understand that you have set a rule to remove the accept-encoding request header but still it is reflected in the browser.

Could you please verify on below things:

1. Please cross-check the rule set created previously, which is properly configured to remove the header. Please verify the action to remove the header is properly defined or not and also make sure that the rule is associated with the correct front endpoint. For your reference: https://learn.microsoft.com/en-us/azure/frontdoor/standard-premium/how-to-configure-rule-set#configure-rule-set-in-azure-portal
2. Make sure that you have given a higher priority to remove the accept-encoding header.
3. Please try to use the different tools (curl, postman) to confirm that the rule is working properly.

      curl -H "Accept-Encoding: gzip" <your_front_door_url>
   

4. For disabling compression on Azure Front Door, please refer: https://learn.microsoft.com/en-us/azure/frontdoor/how-to-configure-caching#:~:text=Optionally%2C%20select%20Enable%20compression%20for%20Front%20Door%20to%20compress%20responses%20to%20the%20client
5. Please try to enable diagnostic logging on your Azure Front Door to get more insights.

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

If the answer is helpful, please click "Accept Answer" and "Upvote it" so that other community members can find the right answers.

Thanks,

Sai Prasanna.