Types of Real Server Monitors
There are several Real Server Monitors available, and the table below explains these. You can, of course, write additional monitors using PERL.
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Monitoring Method
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Description
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Example
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HTTP 200 OK
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A TCP connection is made to the Real Server. After the connection is made, a brief HTTP request is sent to the Real Server.
When the response is received, it is checked for the ‘200 OK’ string. If it is present, the server is considered operational.
Please note that using this monitor fetches the entire page with contents.
This monitoring method can only really be used with HTTP and Accelerated HTTP service types. However, if a Layer 4 Service Type is in use for an HTTP server, it could still be used if SSL is not in use on the Real Server or handled appropriately by the "Content SSL" facility.
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Request
GET / HTTP/1.1
Host: 192.168.159.200
Accept: */*
Accept-Language: en-gb
User-Agent: Edgenexus-ADC/4.0
Connection: Keep-Alive
Cache-Control: no-cache
Response
HTTP/1.1 200 OK
Content-Type: text/html
Last-Modified: Wed, 31 Jan 2018 15:08:18 GMT
Accept-Ranges: bytes
ETag: "0dd3253a59ad31:0"
Server: Microsoft-IIS/10.0
Date: Tue, 13 Jul 2021 15:55:47 GMT
Content-Length: 1364
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<title>jetNEXUS</title>
<style type="text/css">
<!--
body {
color:#FFFFFF;
...
</body>
</html>
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HTTP 200 Head
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A TCP connection is made to the Real Server with the PATH field specifying the location to be checked.
The head portion of the response is fetched from the server, with contents discarded. The response is checked for 200 OK. If it is present, the server is considered operational.
Please note that using this monitor fetches only the head portion.
This monitoring method can only really be used with HTTP and Accelerated HTTP service types. However, if a Layer 4 Service Type is in use for an HTTP server, it could still be used if SSL is not in use on the Real Server or handled appropriately by the "Content SSL" facility.
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Request
HEAD / HTTP/1.1
Host: 192.168.159.200
Accept: */*
Accept-Language: en-gb
User-Agent: Edgenexus-ADC/4.0
Connection: Keep-Alive
Cache-Control: no-cache
Response
HTTP/1.1 200 OK
Content-Length: 1364
Content-Type: text/html
Last-Modified: Wed, 31 Jan 2018 15:08:18 GMT
Accept-Ranges: bytes
ETag: "0dd3253a59ad31:0"
Server: Microsoft-IIS/10.0
Date: Tue, 13 Jul 2021 15:49:19 GMT
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HTTP 200 Options
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A TCP connection is made to the Real Server, and an Options request is made.
The Options are returned and checked for 200 OK content.
If the 200 OK content is found, then the server is deemed to be available.
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Request
OPTIONS / HTTP/1.1
Host: 192.168.159.200
Accept: */*
Accept-Language: en-gb
User-Agent: Edgenexus-ADC/4.0
Connection: Keep-Alive
Cache-Control: no-cache
Response
HTTP/1.1 200 OK
Allow: OPTIONS, TRACE, GET, HEAD, POST
Server: Microsoft-IIS/10.0
Public: OPTIONS, TRACE, GET, HEAD, POST
Date: Tue, 13 Jul 2021 16:23:39 GMT
Content-Length: 0
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HTTP Head
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The HTTP Head monitor allows us to check for a specific value in the Head portion of the HTTP stream. We can enter a Path and Required Response in the appropriate fields and then check for that value in the response.
Should the Required Response value be found in the Head, the server is deemed to be up and available.
We can also use this on specially protected pages that need a username and password. In this manner, the monitor’s result can be deemed to be accurate.
For example, providing /ispagethere.html and 200 OK values in the Path and Required Response fields will return a successful result if the server is up, the page is available, and responds to the request.
This monitoring method can only really be used with HTTP and Accelerated HTTP service types. However, if a Layer 4 Service Type is in use for an HTTP server, it could still be used if SSL is not in use on the Real Server or handled appropriately by the "Content SSL" facility.
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Request
HEAD /ispagethere.htm HTTP/1.1
Host: 192.168.159.200
Accept: */*
Accept-Language: en-gb
User-Agent: Edgenexus-ADC/4.0
Connection: Keep-Alive
Cache-Control: no-cache
Response
HTTP/1.1 200 OK
Content-Length: 1364
Content-Type: text/html
Last-Modified: Wed, 31 Jan 2018 15:08:18 GMT
Accept-Ranges: bytes
ETag: "0dd3253a59ad31:0"
Server: Microsoft-IIS/10.0
Date: Wed, 14 Jul 2021 08:28:18 GMT
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HTTP Options
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The HTTP Options monitor allows you to check for a specific value within the returned Options data.
We enter a Path and Required Response in the appropriate fields and then check the response.
If the Required Response is found in the Options data, the server is available and running.
The Required Response values can be any of the following: OPTIONS, TRACE, GET, HEAD, and POST.
For example, providing /ispagethere.html and GET values in the Path and Required Response fields will return a successful result if the server is up, the page is available, and it responds to the request.
This monitoring method can only really be used with HTTP and Accelerated HTTP service types. However, if a Layer 4 Service Type is in use for an HTTP server, it could still be used if SSL is not in use on the Real Server or handled appropriately by the "Content SSL" facility.
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Request
OPTIONS /ispagethere.htm HTTP/1.1
Host: 192.168.159.200
Accept: */*
Accept-Language: en-gb
User-Agent: Edgenexus-ADC/4.0
Connection: Keep-Alive
Cache-Control: no-cache
Response
HTTP/1.1 200 OK
Allow: OPTIONS, TRACE, GET, HEAD, POST
Server: Microsoft-IIS/10.0
Public: OPTIONS, TRACE, GET, HEAD, POST
Date: Wed, 14 Jul 2021 09:47:27 GMT
Content-Length: 0
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HTTP Response
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A connection and HTTP request/response is made to the Real Server and checked as explained in the previous examples.
But rather than check for a "200 OK" response code, the HTTP response’s header is checked for custom text content. The text can be a full header, part of a header, a line from part of a page, or just one word.
For instance, in the example shown to the right, we specified /ispagethere.htm as the Path and Microsoft-IIS as the Required Response.
If the text is found, the Real Server is deemed to be up and running.
This monitoring method can only really be used with HTTP and Accelerated HTTP service types.
However, if a Layer 4 Service Type is in use for an HTTP server, it could still be used if SSL is not in use on the Real Server or handled appropriately by the "Content SSL" facility.
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Request
GET /ispagethere.htm HTTP/1.1
Host: 192.168.159.200
Accept: */*
Accept-Language: en-gb
User-Agent: Edgenexus-ADC/4.0
Connection: Keep-Alive
Cache-Control: no-cache
Response
HTTP/1.1 200 OK
Content-Type: text/html
Last-Modified: Wed, 31 Jan 2018 15:08:18 GMT
Accept-Ranges: bytes
ETag: "0dd3253a59ad31:0"
Server: Microsoft-IIS/10.0
Date: Wed, 14 Jul 2021 10:07:13 GMT
Content-Length: 1364
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<title>jetNEXUS</title>
<style type="text/css">
<!--
body {
color:#FFFFFF;
…
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Multi-Port TCP monitor
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This method is like the above, except that you can have several different ports. The monitor is deemed successful only if all ports specified in the required content section respond correctly.
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Name: Multi-Port Monitor
Description: Monitor multiple ports for success
Page Location: N/A
Required Content: 135,59534,59535
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TCP Out of Band
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The TCP Out of Band method is like a TCP Connect except that you can specify the port you wish to monitor in the required content column. This port is typically not the same as the traffic port and is used when you want to tie services together
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Name: TCP Out of Band
Description: Monitor Out of Band/Traffic port
Page Location: N/A
Required Content: 555
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DICOM
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We send a DICOM echo using the "Source Calling" AE Title value in the required content column. You can also set the "Destination Called" AE Title value in the Notes section of each server. You can find the Notes column within the IP Services-
-Virtual Services--Server page.
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Name: DICOM
Description: L7 health check for DICOM service
Monitoring Method: DICOM
Page Location: N/A
Required Content: AET Value
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LDAPS
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This new health check is used to check the health and response of an LDAP/AD server.
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Name: LDAPS
Description: LDAP/AD Server health check
Usage parameters are as follows:
Username: cn=username,cn=users,dc=domainname,dc=local
Password: DomainUserPassword
Content: 200OK
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SNMP v2
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This monitoring method allows you to check for a server availability status using the server’s SNMP MIB response.
The Require Response value should contain the Community Name.
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DNS Server Check
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When load balancing DNS Servers, it is helpful to see if the server responds to DNS queries.
The monitor can be used as follows:
· The Path field is used for the FQDN that you are querying. For example, if you wished to query www.edgenexus.io, then enter this in the Path field.
· If you leave this blank, then the monitor will use its default lookup to make the query.
· The Required Response field can be left blank, and the monitor will assume that any response is considered valid. Otherwise, you should enter the expected IP in the Required Response field. For example, this may be 101.10.10.100. If the query returns this value, the monitor flags a success; else, it will flag a failure.
A success result indicates that the DNS server you are load-balancing is operational.
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