Solutions

How to identify which CacheFlow appliance is processing a request

Solutions ID:    KB4345
Version:    1.0
Status:    Published
Published date:    03/24/2011
 

Problem Description

In a load balanced environment, a request can be processed by any of the CacheFlow appliances in the group. It is useful in various circumstances to determine which CacheFlow in the group is processing requests for a specific URL.

Resolution

Identify the CacheFlow appliance that handles a particular URL by creating a policy rule to return an exception page when a request matches a specific identifier phrase. The exception page will specify the IP address of the CacheFlow appliance that handled the request.

The policy to return the exception page identifying the appliance can be specified using the CacheFlow CLI or Policy GUI.

To create the policy using the CLI:

CF5000#inline policy local _oef_
<access>
 url.regex="~~identify_cacheflow~~" exception(identify_cacheflow)
_oef_
  ok

Warning:  If the local policy file is non-empty before making the above change, ensure that you first copy and re-apply the existing local policy as part of the inline command.

 

To create the policy using the Policy GUI:

1.  Access the CacheFlow GUI at https://<CF-IP>:8082/ and click on the Tools tab.
2.  Open the Policy GUI by clicking the link on the left panel and hitting launch on the new page.
3.  Open the Policy menu, select Add Access Layer... and specify a name for the layer.
4.  Right-click the Destination column and select Set from the context menu.
5.  In the Set Destination Object window, click New.
6.  Select Request URL from the menu and specify the name of the object.
7.  In the Add Request URL Object window, select the 'Advanced Match' option.
8.  Enter an obscure phrase in the Path field that is unlikely to be part of a normal request. This is the phrase that will be used to identify the CacheFlow.
9.  Choose Contains from the drop-down box next to the Path field. Scheme can be left as Any and the remaining fields can be left blank.
10.  Click Add to add this request object and then close the window.
11. You should see your newly created request object in the destination object list. Close the Set Destination Object Window by pressing Ok.
12. Right-click on the Action column and select Set from the context menu.
13. In the Set Action Object window, select New.
14. Choose Return Exception from the menu and name the object.
15. Select Built-in exception, to get a list of available exceptions and choose identify_cacheflow from the list.
16. Click OK to close the Add Return Exception Object window and then OK again to close the Set Action Object window.

 

17. Apply this policy by clicking the Install Policy button.

Once policy has been installed, request a website from a browser and include the obscure phrase. For example, if the obscure phrase is “~~identify_cacheflow~~”, then to identify the CacheFlow appliance that handles requests for www.bluecoat.com make a request for

www.bluecoat.com/~~identify_cacheflow~~

The response will be an exception page containing the IP address of the CacheFlow appliance that processed the request.

It is important to use an obscure, unique phrase that is unlikely to be an actual website address. This will prevent users from hitting unintentional exception pages.

Since each request is independently load-balanced, this appliance determination method will only work with destination or domain hashing.  If URL hashing is used, this method cannot reliably determine the correct CacheFlow appliance.

 


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