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Teddy_Brewski's avatar
Teddy_Brewski
Icon for Altocumulus rankAltocumulus
Mar 06, 2026

Question about healthchecks

Hello, We're publishing quite old server behind XC load balancer, and to make it work I had to lower "TLS Security Level" to Medium under Origin Pool > TLS. This works fine, however, without health...
F5 Distributed Cloud
healthcheck
xc
Nikoolayy1's avatar
Nikoolayy1
Icon for MVP rankMVP
Mar 07, 2026

The XC health checks use the same ciphers that you client traffic uses so if the client traffic can connect to the test web page without an issue it is not that. You can stop the health checks and try to connect to the test web page with a browser or postman through the Virtual server.

Add also the correct hostname is configured and under the health checks maybe stop or enable HTTP/2 .

 

See the links below as well

 

https://my.f5.com/manage/s/article/K000147503

 

https://my.f5.com/manage/s/article/K000156742

 

A quick post on how F5 XC Health Checks are different from BIG-IP | DevCentral

 

Teddy_Brewski's avatar
Teddy_Brewski
Icon for Altocumulus rankAltocumulus
Mar 07, 2026

Thank you Nikoolayy1​ 

If I disable the healthcheck I can access the web page without any issues.

My case is exactly how it's described in K000156742:

 

Answer/Recommended Actions

  • [Origin Pools][Origin Servers]                                                                                                        : IP address
  • [Health Check Parameters][Health Check HTTP Request Parameters][Specify Host Header]: Host Header Value (e.g., bbb.example.com)
  • Actual Host header in HTTP request                                                                                           : bbb.example.com

 

Behavior:

If you wish the Host header to contain a specific hostname, you must manually provide it in the "Specify Host Header" setting when your origin is configured with an IP address. This allows requests to pass the proper Host value to your backend.

 

The origin server is the IP.  If I define the healthcheck and specify the hostname (publicly resolvable FQDN), I can't access the web page anymore -- the error is "503 Service Unavailable".  I do not see any connection attempts in the web server logs of the backend server.