The HTTP-ECV monitor fails and returns the 404 Not Found response code.

For example, a monitor of the HTTP-ECV type was configured to monitor the status of a backend server using the following as the expected response string:
"Response is Successful."

The status of the related service was marked as DOWN and the monitor returned the 404 Not Found response code. However, when the user accesses the webpage directly from a web browser, the webpage displays the expected response string successfully, as shown in the following screen shot. 

To resolve this issue, modify the monitor to send a Host header as part of the Custom Header information to the back-end server. The following screen shot has the sample configuration for the HTTP-ECV monitor.

Problem Cause

By default, an HTTP-ECV monitor inserts a Host header using IP address of the server. The monitor inserts the Connection as Close.

These headers are separated by a carriage-return and new-line characters, such as “\r\n”.

The following is the sample HTTP header from a web browser for reference:

GET /health_monitor_test.htm HTTP/1.1
Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, application/x-shockwave-flash, application/x-silverlight, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, application/x-ms-application, application/x-ms-xbap, application/vnd.ms-xpsdocument, application/xaml+xml, */*
Accept-Language: en-us
UA-CPU: x86
Accept-Encoding: gzip, deflate
If-Modified-Since: Thu, 15 Jul 2010 18:20:47 GMT
If-None-Match: "c0629d724a24cb1:0"
User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; .NET CLR 1.1.4322; .NET CLR 2.0.50727; InfoPath.2; OfficeLiveConnector.1.3; OfficeLivePatch.0.0; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)
Host: example.com
Connection: Keep-Alive

HTTP/1.1 304 Not Modified
Last-Modified: Thu, 15 Jul 2010 18:20:47 GMT
Accept-Ranges: bytes
ETag: "c0629d724a24cb1:0"
Server: Microsoft-IIS/7.5
X-Powered-By: ASP.NET
Date: Mon, 19 Jul 2010 15:14:37 GMT

The following is the sample Host header from a HTTP-ECV monitor for reference:

GET /health_monitor_test.htm HTTP/1.0
Host: 10.217.153.19
Connection: Close

HTTP/1.1 404 Not Found
Content-Type: text/html
Server: Microsoft-IIS/7.5
X-Powered-By: ASP.NET
Date: Mon, 19 Jul 2010 15:39:39 GMT
Connection: close
Content-Length: 1245

The following screen shot displays the Standard Parameters tab of the Configure Monitor dialog box of the monitor on which the issue was observed.

Notice that the Custom Header field is empty.

CTX120921 - How to Configure HTTP-ECV Health Monitor for Internet Proxy Servers
CTX205406 - How to use HTTPS-ECV health check monitor on NetScaler