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LTM Health Monitors


Hi team. I want to ask a question about health monitors.


I have a Web site ( behind the Load Balancer. I created a health monitor and I wrote send string :

''GET / HTTP/1.1\r\\r\nConnection: Close\r\n\r\n''

I wrote recieve string : HTTP 1.1 200 OK


And application is avaliable. VS is online (green circle)


Then I changed receive string to : ''GET / HTTP/1.1\r\\r\nConnection: Close\r\n\r\n. So I replaced host with an unrelated name.


And application is available again 🙂 VS is online (green circle)


How should we interpret this? Do you know good article or videos about send and recieve string?


Thank you..





All you need to kown is describes here :

in an HTTP 1.1 request, the Host header is required, although it may contain a null value





HI, its actually quite simple, if you have web server, which hosts only one web application and listent to all incoming web requests (not checking HTTP 'Host' header), then of course it'll be successful. For example, when you're first starting new web server on IIS or Apache, they both have default landing page with platform information. So your year health monitor will definitely work for that page.


I suggest you to turn on Health monitor logging and then check logs in /var/log/monitors/ directory. Also you can test your health monitor via curl utility. You can test it directly with your web server, without f5 and will see that the very same request string will be successful.


So, in short, you should check the configuration on your web server's side, if it's apache, you can look at this url: