Re: how to achieve URL hash LB algorithm on ZXTM

Thanks Ben
it works like a charm!! TrafficScript is quite impressive. any idea about
how TrafficScript impacts the performance of ZXTM?



On Thu, Jul 30, 2009 at 6:33 PM, Ben Mansell <[email protected]> wrote:

> That is what it achieves. It does this by using a session persistence
> mapping that picks a server to use based on the URL requested, and not on
> the client.
>
>
> Ben
>
> On 30/07/2009 06:45, Eric Y. Zhang wrote:
>
>> thanks. but that is not what I really want. the trafficscript divided
>> traffic based on session, I want something like this
>>
>> www.abc.com/1.html<http://www.abc.com/1.html>  on squid1 permanently
>> www.abc.com/2.html<http://www.abc.com/2.html>  on squid2 permanently
>>
>>
>> Eric
>>
>> On Wed, Jul 29, 2009 at 5:19 PM, Ben Mansell<[email protected]<mailto:
>> [email protected]>>  wrote:
>> On 29/07/2009 00:48, Eric Y. Zhang wrote:
>> routing requests to different backend server in same pool.let's say, I
>> have 5 squid servers behind LB, if LB can do URL hash, then 1of squid server
>> only needs take 20% requests, that helps a lot.
>>
>> There are a few ways to achieve this. The first is to use the 'perceptive'
>> load balancing algorithm. This takes several factors into account when
>> choosing a node to use, including the URL of a request. However, it's only
>> one of many factors, so it doesn't rigidly enforce the URL->squid server
>> mapping that you probably want.
>>
>> What you can do instead is to leave the LB algorithm unaltered, and
>> instead use a session persistence class to dictate where each request goes.
>>
>> Create a 'Universal' session persistence class and assign it to your pool
>> of squid servers. This then lets a TrafficScript rule pick which squid
>> server to use. The TrafficScript command is:
>>
>> connection.setPersistenceKey( http.getRawURL() );
>>
>> ...and then requests with the same URL will use the same squid server.
>> However, this needs a bit of refinement. You are likely to have many many
>> different URLs going to your squid servers. Each different URL creates a
>> different session persistence mapping, and there are limits on the number of
>> these. To ensure that too many aren't used, we can 'hash' the URL into a
>> smaller set of sessions:
>>
>> # Hash the URL, then take the first byte, giving 256 different sessions.
>> # This also uses the website hostname, in case you are caching several
>> # websites.
>> $session = string.left( string.hashMD5( http.getHostHeader() .
>>                                        http.getRawURL() ), 1 );
>> connection.setPersistenceKey( $session );
>>
>> So, add this rule in, assign it to your virtual server and then your squid
>> traffic will be nicely divided up. This should improve the cache hit rates.
>>
>>
>> Ben
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>>
>> --
>> Life is hard
>>
>
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