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From Leif Hedstrom <zw...@apache.org>
Subject Re: traffic server cache key
Date Wed, 14 May 2014 21:16:55 GMT

On May 13, 2014, at 12:14 PM, Daniel Biazus <daniel.biazus@azion.com> wrote:

> Hi Guys,
> 
>     We've been using traffic server as a reverse proxy to delivery static content across
multiple CDN nodes, though the regex purge works as expected through web UI tool, We've been
facing some challenges regarding the cache keys when the objects are stored in cache.
>     In order to have a better understanding of our scenario, let's take a look at this
example:
> 
> Scenario 1:
> 
> - traffic server is working as a reverse proxy:
> 
> #remap.config
> 
> map http://finalurl.foo.bar/   http://originserver.foo.bar/
> reverse_map  http://originserver.foo.bar/  http://finalurl.foo.bar/
> 
> - We have to purge all css files under the URL http://finalurl.foo.bar/
> 
> Considering this, we have to purge the following regex:
> 
> - http://finalurl.foo.bar/*.css
>     
> The example above doesn't work due the fact that traffic server uses the origin URL to
calculate the hash key, then, in this case we have to make a purge request using the origin
server URL (that's not nice with our clients, right ?):
> 
> - http://originserver.foo.bar/*.css
> 
> So guys, anyone knows if there is a way to change the hash key in traffic server, or
even if is there some workaround to deal with this scenario ?


The common way of doing this is to have a plugin, that generates cache keys based on a combination
of the URL and a generation ID. This would easily be configurable per remap rule, such that
you can then instantly (O(1)) purge all objects for that remap rule simply by modifying (increasing)
the generation ID. There is one such plugin in the public domain, although it probably needs
a little loving. :) An easy adoption to that plugin would be to take the generation ID as
an argument on the remap rule.

— Leif


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