Re: how to achieve URL hash LB algorithm on ZXTM

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 on squid1 permanently
www.abc.com/2.html on squid2 permanently


Eric

On Wed, Jul 29, 2009 at 5:19 PM, Ben Mansell <[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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