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From Bernd Koecke>
Subject Re: PROPOSAL: mod_jk2: Group/Instance
Date Tue, 30 Apr 2002 08:14:53 GMT
Hi Costin,

some weeks ago I send a patch for mod_jk for an only routing lb_worker. A few 
days later I sent the docu. Henry Gomez said, that it should be commited. But it 
I think it isn't in the repository. But its the same  with me here, to mutch 
work for to less time :).

Again an example of my environment:
Cluster with 4 nodes, tomcat and apache on every node.
One Loadbalancer in front of the cluster which does a simple round robbin.

I need sticky sessions but no loadbalancing in the module. If a request without 
a session comes in, it should be routed to the _local_ tomcat.

I think this could be possible with the associated instance of a channel (item 
7). Then I have to configure all four nodes for the same group. Because all 
nodes will serve the same webapps and associate the channel with this group. But 
for this I need a non balancing group. I don't see if the default behavior of a 
group is balancing and if this can be switched off. Is this right or do I miss 


Bernd wrote:
> One of the major goals of mod_jk2 is simpler configuration. 
> This proposal will cover the 'workers'.
> 1. The 'worker' name is deprecated. It refers to too many
> things in mod_jk, and causes too much confusion ( i.e. it
> is a 'handler', coresponds to a jvmRoute, a protocol, a
> channel ).
> 2. We'll use the term 'channel' to define the connections 
> between jk and tomcat. Each channel will follow a standard 
> naming syntax:
>    channel.socket:HOST:PORT
>    channel.unix:/PATH
>    channel.jni:jni
> Altenatively, the local part can be used as a shortcut.
> Each channel will use Ajp13 protocol by default ( or whatever
> is specific to the transport, or overriden ).
> 3. We'll use the term 'instance' ( XXX or a better name 
> if you can sugest one ) to refer to a single tomcat VM. 
> That's what will be used in the jvmRoute. A tomcat instance
> can be reached by multiple channels. 
> By default, each instance will have one socket channel and
> will be named by the local part ( i.e. HOST:port ). That's the
> name that'll identify the VM.
> 4. We'll use the term 'group' to reffer to a set of tomcat
> 'instances' that share a number of applications. The default
> group will be called 'lb'.  One 'instance' can be part of 
> one or many groups. 
> 5. Each URI will be associated with a 'group'. In what used to
> be: 
>   JkMount /examples ajp13
> the 'group' will replace ajp13. 
> As I said, the default group is called 'lb' and includes all
> tomcat instances that are defined. 
> For each application that is installed on all instances, the 'lb'
> group must be used.
> If you have a sophisticated setup - and an app is installed
> only on some instances, you can use names like "lb_examples", 
> and explicitely define what tomcat instances belong to the group.
> 6. The webapps will be defined by a hierarchy of directories
> ( host/webapp_name ) ( see previous mail ). Each webapp
> is obviously mapped consistently to one group, which will be 
> defined inside the WEB-INF/jk2/ 
> 7. Each channel will have an associated 'instance' ( it can't
>  go to 2 tomcats ) and groups. The lb configuration is 
> done automatically based on those attributes. The mappings 
> are done automatically based on the hierarchy. If no
> is found, the whole webapp will be forwarded to the default
> group ( the common case ).
> I believe this model covers all current use cases. Please, please,
> send feedback and let me know if you can help ( implementation,
> documentation, testing ), but feedback is the first step.
> Costin 
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Dipl.-Inform. Bernd Koecke
Schlund+Partner AG
Fon: +49-721-91374-0

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