Re: how to achieve URL hash LB algorithm on ZXTM

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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