How do I prevent a CacheFlow device from caching (storing local copies of) certain content?
Article ID: 166128
Updated On:
Products
Issue/Introduction
How do I prevent caching of certain content?
How do I prevent caching of content in response to a take-down notice?
Resolution
Your CacheFlow appliance provides a local policy gesture which allows you to prevent caching of content based on the set of rules you specify. When used, this gesture allows the cache to be bypassed – both for content lookup and for content storage. This means that the content will not be served from cache if it’s already there, nor will it be stored in cache if it’s not there previously.
Specifically, by using this gesture in policy, you can do things like
- prevent caching of entire domain
- prevent caching of certain file name on a certain domain
- prevent caching of a very specific youtube video
- etc.
Local policy allows you to prevent caching of content based on various pieces in the HTTP request.
General rules to prevent caching and lookup of content can be generalized as:
1.) Identify something unique about the request for the content you would like the appliance to not cache.
2.) Use local policy and the ‘exclude’ gesture to prevent the appliance from caching that content.
Here are particular examples:
1) Prevent caching of the entire sharefiles.com domain using your Visual Policy Manager
a. Add a new ‘Access’ layer
b. Set the destination to ‘sharefiles.com’
c. Set ‘Suppress Caching’ as the action
d. Click ‘Install Policy’
2) Prevent caching of a certain youtube video using local policy
Let’s assume that you would like to prevent the appliance from caching: ‘http://www.youtube.com/watch?v=FxKuSkZxE204’.
This video page ultimately sends an HTTP request for the actual flash video content, which will look something like
‘http://v10.lscache3.c.youtube.com/videoplayback?sparams=id%2Cexpire%2Cip%2Cipbits%2Citag%2Calgorithm%2Cburst%2Cfactor%2Coc%3AU0dYSlJPUl9FSkNNOF9KSVZB&fexp=905225&algorithm=throttle-factor&itag=34&ipbits=0&burst=40&sver=3&signature=9624B87F1F3EC9C9CD69007A9F3979C7D6DFE533.31ACDB32702690198C0FB6BD8DD0F86B879F662C&expire=1295244000&key=yt1&ip=0.0.0.0&factor=1.25&id=1712ae4a4671136e&’
The URL for the flash content is dynamic in nature, but one parameter in the query stays static to identify which video to serve. This id is in bold in the above example. You can use that id to prevent the appliance from caching this very specific video. In particular:
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; Sample CPL to exclude a very specific youtube video
<access>
url.domain=youtube.com url.query.substring=”id=1712ae4a4671136e” exclude(yes)
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3) Prevent caching of a certain filename at rapidshare
If, for legal reasons, you need to prevent caching of a certain filename from filesharing sites like rapidshare.com, you can use the following CPL syntax:
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<access>
; Sample CPL to exclude all instances of ‘Avatar.mp4’ from rapidshare.com
url.domain=rapidshare.com url.substring=’Avatar.mp4’ exclude(yes)
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This policy is useful if you would like to prevent caching of ‘Avatar.mp4’ from rapidshare and will work even if multiple users uploaded the file.
It’s important to remember that a consequence of preventing content from being cached by the appliance is that the appliance can no longer obtain bandwidth savings for object(s) excluded.
For example, let’s assume you chose to exclude a very popular (viral) youtube video, which is 10 Mb in size. If this video is requested tens of thousand times over a period of one week by different clients going through your CacheFlow appliance, you could loose hundreds of gigabytes of saved server side bandwidth because the video is excluded from your appliance’s caching mechanism.
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