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From Jules Gosnell <>
Subject Re: WADI integration
Date Sat, 10 Dec 2005 12:34:58 GMT
Jeff Genender wrote:

> Dave,
> Thanks for noticing ;-)
> Dave Colasurdo wrote:
>> I see that WADI has recently been integrated into Geronimo.
>> Great Job!!!
>> Can someone please provide a quick high level description of what 
>> is/isn't available from WADI in Geronimo v1?
>> Tomcat clustering
> Yes
>> Jetty clustering
> Yes
>> Load Balancing
> Yes through AJP
> I will let Jules go into the rest when he wakes up and give a proper 
> response.

Thanks, Jeff,

Load-balancing :

We don't ship our own load-balancer. WADI's philosophy is that the 
load-balancer is part of the deployment environment into which it must 
fit. WADI will work with any load-balancer. It is likely that companies 
will have spent thousands of dollars on state of the art hardware and 
will not want to be constrained into running a free java load-balancer 
on a linux box, just so that they can run WADI. Many open source 
load-balancers are available, if you are not in this situation. Apache 
HTTPD/Mod_JK is  common solution.

>> HttpSession failover
This is implemented by maintaining and frequently refreshing redundant 
off-node copies of session data.

We have a preliminary impl in place, but it is only hooked up to a DB 
backend - full in-vm replication is the goal - a cuple of months away, 

>> -file based
We have a file-system based persistant store - this could be extended 
for replication.

>> -database
We have a store, tested on mysql, that can be used for long-term 
persistance, paging and replication - slow.

>> -mem to mem (one to all)
You will be able to do one to all - but it is not the intended default - 
it doesn't scale further than a few nodes.

>> -mem to mem (one to one/several)
This is the current plan. I expect most sites to maintain one or two 
redundant copies. This should increase session availability sufficiently 
for most deployments.

>> -distributed cache
specifically for sessions - running, but not yet production-ready. The 
Getting Started guide on the website, will, when it is published (over 
the next few days) walk you through examples.

generalised, for use with application space POJOs - via a JCache API - 
on the roadmap, but NYI.

>> Sticky Session
Depends on the load-balancer. We have an integration for mod_jk. More 
integrations (just a pluggable class) will be written as and when the 
need arises. They will generally just manipulate cookies or the session 
id. Many load-balancers that are simply associating cookies with nodes 
internally, will not need any form of integration, they will just work .

>> Cluster membership (manual, auto-discovery)
Auto-discovery - we sit on top of activecluster which provides services 
such as the cluster abstraction, membership change notification and 
death detection. On top of this WADI provides a self-partitioning, 
self-healing substrate, the basis of a distributed hash table in which 
sessions are and later POJOs will be stored.

>> Centralized/independent mgmt
Currently independant, I guess - via JMX, with which WADI components may 
be registered as they are built by Spring, via their JMX Exporter. We 
have opened various channels to talk about centralised management, but 
have no concrete design as yet.

>> Deployment (independent, centralized, farming)
In my peripheral vision, not currently a core part of WADI, although 
definitely required for Geronimo clustering. This is part of some wider 
discussions which need to be held soon. Exactly how WADI core or 
extended technology may be fitted into this remains to be decided.

>> Anything above Web Tier clustering?
Yes. We have started our OpenEJB SFSB integration. SFSBs, in clustering 
terms, behave very similarly to HttpSessions. Gianny Damour is working 
on this. It won't be in Geronimo-1.0, but we hope that it is not too far 
away. We are also looking at application-server level abstractions, such 
as User and Application level sessions, which will allow Geronimo to 
maintain the colocation of all resources related to a user or a 
user/application interaction. The POJO stuff discussed above will give 
us application space capability. Then we are left with things like 
farmed deployment etc, that you have also mentioned.

>> Thanks
>> -Dave-
Hope that helps, Dave.

If you are at ApacheCon, I shall be around from monday til thursday - 
drop me a mail and we can hook up.


"Open Source is a self-assembling organism. You dangle a piece of
string into a super-saturated solution and a whole operating-system
crystallises out around it."

 * Jules Gosnell
 * Partner
 * Core Developers Network (Europe)
 * Open Source Training & Support.

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