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CSS polling and response from servers


Is it possible to poll webservers from CSS for a specific content on the webpage.

At present we poll for a URL. what we want to ensure if the web page is modified then CSS should take server out of farm.

Also all these web pages have drop down box and connects to a DB server when a select is made. whats the best practice to implement if these drop down doesnt work , where the web server lost the connection DB server the CSS no longer sends the request to that server



Re: CSS polling and response from servers


The CSS 11000 HTTP keepalive uses one of two available methods:



They are specified by using the method command while in the keepalive configuration mode (config-keepalive).

When an HTTP HEAD keepalive is issued in the CSS 11000, a 200 Status OK is expected in the response packet from the server it is querying. If the 200 OK status is not returned, the CSS 11000 considers the service down. If the CSS 11000 receives any other status code such as a 404 Object Not Found or a 302 Object Moved, the CSS 11000 will view this as an incorrect response and mark this service as down. The head method is the default. The CSS 11000 does not compute a reference hash value for this type of keepalive.

When an HTTP GET keepalive is used, the CSS 11000 expects not only to see the 200 Status OK in the response packet, but it will also run a checksum on the entity body. The first time the CSS 11000 goes out to query, the server will run a checksum on the entity body and store that hash value for future queries. If future responses pass back a 200 Status OK and the hash value that is calculated is different from the stored value, then the service is considered down. If the 200 Staus OK is not returned, or if the 200 OK status is returned but the hash value is different from the reference hash value, the CSS 11000 considers the service down.

When you specify an URL for an HTTP keepalive, the CSS 11000 calculates a hash value for the Web page specified in the URL. If the Web page changes, the hash value no longer matches the original hash value, and the CSS 11000 assumes that the service is down. To prevent the CSS 11000 from assuming that a service is down because of a hash value mismatch, specify the keepalive method as the head. Because of the nature of HTTP GET keepalives and the way they are calculated, do not use them on dynamically changing pages because their checksums change constantly.

With CSS if you use GET method in a keepalive, It hashes the page and if the subsequent GET requests gives a different hash the service is marked down.

Here is an example:

service WEB01

ip address

keepalive method get

keepalive type http

keepalive uri "/General/GenAppAlive.asp?ControlAction=InitialLoad"


Sachin Garg

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