By default, NSX Advanced Load Balancer appends additional HTTP headers (Host, User-Agent and Accept) into HTTP health monitor requests.

The exact values of these headers are as follows:

Header

Values

User-Agent

avi/1.0\r\n

Host

<hostname>\r\n

Accept

*/*;\r\n\r\n
For instance, if an admin (user) adds a Host header in HTTP Client Request Header field of a health monitor, NSX Advanced Load Balancer will send this additional Host header together with the existing Host header (Host header inserted by NSX Advanced Load Balancer).

To prevent adding additional host headers, in the HTTP or HTTPS Health Monitors, select Use Exact Request in the NSX Advanced Load Balancer UI.

Alternatively, you can configure the health monitor to instruct NSX Advanced Load Balancer to pass the exact HTTP request string as specified by the admin (user), without any automatic insertion of the additional HTTP headers using the CLI.

This indicates that user is now responsible for adding the appropriate headers to the HTTP client request field.

Configuration from NSX Advanced Load Balancer CLI

Login to NSX Advanced Load Balancer CLI, and use configure healthmonitor System-HTTP command to change the value of the flag exact-http-request.

[admin:10-1-1-1]: > configure healthmonitor System-HTTP
[admin:10-1-1-1]: healthmonitor> http_monitor                                   
[admin:10-1-1-1]: healthmonitor:http_monitor> http_request                                                     
[admin:10-1-1-1]: healthmonitor:http_monitor> http_request "HEAD / HTTP/1.0\r\n\r\n"
Overwriting the previously entered value for http_request
[admin:10-1-1-1]: healthmonitor:http_monitor> exact_http_request
Overwriting the previously entered value for exact_http_request
[admin:10-1-1-1]: healthmonitor:http_monitor>
[admin:10-1-1-1]: healthmonitor:http_monitor> save
[admin:10-1-1-1]: healthmonitor> save

Configuring through UI

Navigate to Templates > Profiles > Health Monitors, click the edit icon to edit health monitors. Choose the desired HTTP health monitor, select the check box for Use Exact Request and click Save.