Can I monitor web servers behind a load balancer?

If you have multiple HTTP servers sitting behind a load balancer, you can still monitor them individually if they are reachable via a public IP address - even if they host multiple domains.

To achieve this, your monitoring configuration needs to make an HTTP request directly to the web servers' IP address instead of the load balancers' IP address.

Because many web servers inspect the Host: request header (for name based virtual-hosting), you will most likely want to override this request header so it contains your domain name rather than the IP address of the server.

You can achieve this configuration with the Wormly HTTP monitoring sensor. Simply put your web servers' public IP address in the URL field, e.g:

http://123.123.123.123/my_app

And specify your Host: header in the Custom Request Headers field, e.g:

Host: www.example.com

By overriding the Host: header, the web server will treat the above request in the same way as if the client had requested the URL http://www.example.com/my_app directly.


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