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From Jeff Genender <>
Subject Re: Clustering
Date Sat, 15 Oct 2005 21:36:53 GMT

Jules Gosnell wrote:
> Jeff Genender wrote:
>> Jules,
>> Thanks for the update.  I like whats been done.  Do you think WADI is 
>> ready begin becoming a part of Geronimo? (i.e ready for prime time)
> I have lots more to do, but I would certainly be interesting in starting 
> integration work with Geronimo. I always had Geronimo in mind whilst 
> working on WADI, it has just been that, until certification, simply 
> implementing specs correctly has been foremost on the G agenda. Now that 
> we have reached this goal, the next one becomes enterprise-readiness. I 
> hope that WADI can help with this. Would you, or anyone else on the 
> list, be interested in taking a look at it and getting involved in the 
> integration ?

Yes...very much so. I would be interested in being one of the key people 
on count me in ;-)

In the mean time I have integrated Tomcat's clustering as an interim.  I 
need to test it, then I will check it in.  But ultimately, I think WADI 
looks to be a great solution for us.

> Jules
>> Jeff
>> Jules Gosnell wrote:
>>> Jeff Genender wrote:
>>>> Now that we have achieved the covetted J2EE Certification, we need 
>>>> to start thinking about some of the things we will need to have in 
>>>> Geronimo in order to be mass adopted by the Enterprise.
>>>> IMHO, I think one of the huge holes is clustering.  This is a heavy 
>>>> need by many companies and I believe that until we get a powerful 
>>>> clustering solution into G, it will not be taken as a serious J2EE 
>>>> contender.
>>>> So, with that said, I wanted to start a discussion thread on 
>>>> clustering and what we need to do to get this into Geronimo.  I 
>>>> personally would like to be involved in this (thus the reason for me 
>>>> starting this thread) - yeah, since Tomcat is done, now I am bored ;-).
>>>> I was going over the lists and emails and had some great discussion 
>>>> with Jules on the WADI project he has built.  This seems compelling 
>>>> to me.  I also noticed Active Cluster as a possibility.
>>>> So lets start from the top.  Do we use an already available 
>>>> clusering engine or do we roll our own?  Here is a small list of 
>>>> choices I have reviewed and it is by no means complete...
>>>> 1) WADI
>>>> 2) Active Cluster
>>>> 3) Leverage the Tomcat Clustering engine
>>>> So here are some of my questions...
>>>> How complete is WADI and Active Cluster?  Both look interesting to 
>>>> me. My only concern with Active Cluster is it seems to be JMS based, 
>>>> which I think may be slow for high performance clustering (am I 
>>>> incorrect on this?).  How mature is WADI?
>>> Here is a status report on WADI.
>>> I'm developing it full time.
>>> A snapshot is available at - documentation is in 
>>> the wiki - at the moment the documentation (rather minimalist) is 
>>> more up to date than the snapshot, but I will try to get a fresh one 
>>> out next week.
>>> WADI is a plugin HttpSession Manager replacement for Tomcat-5.0/5.5 
>>> and Jetty-5.1/60 (it can actually migrate sessions between all four 
>>> in the same cluster).
>>> It comprises a vertical stack of pluggable caches/stores (memory, 
>>> local disc, db etc) through which sessions are demoted as they age 
>>> and promoted as and when required to service a request.
>>> This stack may be connected horizontally to a cluster by inserting a 
>>> clustered store, which uses a distributed hash table (currently 
>>> un-replicated, but I am working on it) to share state around the 
>>> clusters members in a scalable manner. WADI has a working mod_jk 
>>> integration.
>>> WADI currently sits on top of ActiveCluster, which it uses for 
>>> membership notification and ActiveMQ which is used for transport by 
>>> both layers. ActiveMQ has pluggable protocols, including a peer:// 
>>> protocol which allows peers to talk directly to one another (this 
>>> should put to bed fears of a JMS based solution not scaling - 
>>> remember, JMS is just an API). So you do not need to choose between 
>>> WADI and ActiveCluster - they are complimentary. ActiveCluster can 
>>> also (I believe) use JGroups as a transport - I haven't tried it.
>>> ActiveSpace is another technology in this area (distributed caching) 
>>> and it looks as if WADI and ActiveSpace will become more closely 
>>> aligned. So this may also be considered a complimentary technology.
>>> Both Tomcat and Jetty currently have existing clustering solutions. I 
>>> looked closely at the Tomcat solutions before starting out on WADI 
>>> and knew all about the Jetty solution, because I wrote it :-). WADI 
>>> is my answer to what I see as shortcomings in all of the existing 
>>> open source approaches to this problem-space.
>>> Some parts of WADI should soon (December) be undergoing some serious 
>>> testing. When they pass we will be able to consider them production 
>>> ready. Others, notably the distributed hash table are still under 
>>> development (although a fairly functional version is available in the 
>>> I think that, in the same way Tomcat clustering could be enabled 
>>> easily in Geronimo, WADI could also be added by virtue of its 
>>> integration with Tomcat/Jetty, but I have been concentrating on my 
>>> distributed hash table too hard. If anyone is interested in talking 
>>> further about WADI, perhaps trying to plug it into Geronimo (It is 
>>> spring-wired and uses spring to register its components with JMX. I 
>>> guess it should be simple to hook it into the Geronimo kernel in the 
>>> same way, I just haven't had the time), or helping out in any way at 
>>> all, I would be delighted to hear from them.
>>> I have broached the subject of a common session clustering framework 
>>> with members of the OpenEJB team and we have discussed things such as 
>>> the colocation of HttpSessions and SFSBs. I believe OpenEJB has been 
>>> moving towards JCache to facilitate the plugging in of a clustering 
>>> substrate. My distributed hash table is also moving in the same 
>>> direction.
>>> I hope that gives you all a little more information to go on. If you 
>>> have any questions, just fire away,
>>> Jules
>>>> Thoughts and opinions are welcomed.
>>>> Jeff

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