Re: how to achieve URL hash LB algorithm on ZXTM

Thanks for quick reply, Ben.

I was going to do this dynamically, but since I can not get active nodes
list from traffic script, so I have to try your way.

It is not very convenient, if I will add squid server. but it is ok to hard
code server list.


Eric

On Tue, Aug 11, 2009 at 8:53 PM, Ben Mansell <[email protected]> wrote:

> If you want to *always* balance the same URLs to the same server, then this
> can be done too:
>
> 1) Create a session persistence class, this time of type 'Named node', and
> assign it to your pool of squid servers.
> 2) Now, use a TrafficScript rule similar to this to pick the node to use:
>
> # Set this to the number of Squid servers
> $nodes = 2;
> # Hash the URL to a node to use
> $hash = lang.ord( string.hashMD5( http.getHostHeader() .
>                                  http.getRawURL() ));
> $hash = $hash % $nodes;
> if( $hash == 0 ) {
>   connection.setPersistenceNode( "server1:80" );
> } else if( $hash == 1 ) {
>   connection.setPersistenceNode( "server2:80" );
> }
>
>
> This will force ZXTM to use the same backend for each URL. There is no big
> storage mapping URL -> server, it is all done algorithmically.
>
> If a squid server fails, you can control what ZXTM should do via the
> 'failure mode' for the session persistence class. For example, make it pick
> another node to use. When the original server comes back online, it will
> start to be used again.
>
>
>
>
> Ben
>
>
> On 11/08/2009 11:08, Eric Y. Zhang wrote:
>
>> Thanks Ben.
>>
>> so there is no way for me always to balance same URLs into same squid
>> server. I am thinking to get it done by Java extension(coz I can use
>> getNodes in Java) . The input of java extension is URL, output is the
>> $nodename which I should send traffic into.
>>
>>
>>
>>
>>
>>
>> On Tue, Aug 11, 2009 at 4:11 PM, Ben Mansell<[email protected]<mailto:
>> [email protected]>>  wrote:
>> It is 'by design' that the TrafficScript rule hashes the URLs into ~65000
>> different 'buckets', but that you should configure ZXTM to remember fewer
>> mappings than this.
>>
>> ZXTM will store the mappings whatever their value, but will only remember
>> the most recently used mappings. In this way, over time the maps of old URL
>> ->  squid server will slowly be forgotten, and a new server will be picked
>> when that URL is seen again.
>>
>> This will let ZXTM load balance the workload and ensures that any spikes
>> of workload across the cluster will be smoothed out over time.
>>
>>
>> Ben
>>
>>
>>
>> On 07/08/2009 12:18, Eric Y. Zhang wrote:
>> Hi Ben
>>
>> $session = string.left( string.hashMD5(
>> http.getHostHeader().http.getRawURL() ), 2 ); is always bigger than
>> universal_cache_size; so when one new URL not in universal cache comes in,
>> ZXTM will balance it using the algorithm I set in the pool?
>>
>> because I don't have enough memory to store all persistence keys into, so
>> that would be a  problem.
>>
>>
>> another interesting question is do you implement the URL hash on your
>> appliance device?
>>
>>
>> I checked iRule from Devcentral of F5 and tried to convert that election
>> Hash into traffic script, but it seems there is no function in traffic
>> script to list active nodes of a pool.
>>
>> thanks
>>
>> Eric
>>
>>
>> On Fri, Aug 7, 2009 at 10:02 AM, Eric Y. Zhang<[email protected]
>> <mailto:[email protected]><mailto:[email protected]<mailto:
>> [email protected]>>>   wrote:
>>
>> thanks to all of you who discuss this. I learned to many from your
>> threads. this is the most helpful mailing list I ever been.
>>
>> I will try to figure out the best way to spread load/maintain the
>> availability.
>>
>> thanks again
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>>
>> --
>> Life is hard
>>
>
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