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    <p>It's not what JavaRebel does. JavaRebel (according to description) hot-replaces the classes in memory. It's not acceptable in the case of existing connections to the system, since the updated classes may break the client's logic.</p> <p>Once a company I was working for had a similar problem, and it was solved this way:</p> <ul> <li>a smart router was used as a load-balancer</li> <li>the new version was deployed to 50% of the nodes of the (new) cluster</li> <li>new connections were delivered strictly to these updated nodes, old ones were balanced between old nodes</li> <li>old nodes were took off-line (one-by-one, to keep number of clients per node within limits)</li> <li>at the same time, new version was deployed to off-line "old" nodes and they were brought up as new nodes</li> <li>due to EJB clustering, the sessions and beans were picked up by other old nodes</li> <li>eventually (in a few hours), only one old node left, having a single instance of old version and all clients using old version were connected to it</li> <li>when the last old client got disconnected, that node was too brought down</li> </ul> <p>Now, I'm not a networking guy, and cannot give you many details (like what was the router hardware and such). My understanding this can be set up pretty easy, except, if I remember right, we had to setup an additional Weblogic domain to deploy new versions of the application (otherwise it would be conflicting with the old one on JNDI names). </p> <p>Hope that helps.</p> <p>P.S. Ichorus provided a comment saying that the app is deployed on clients' servers. So the router trick may be not feasible. Now, I see only one viable solution right now ( it's 21:52 now, I may overlook things :) ) -- </p> <ul> <li>Develop new version with "versioned" JNDI names; e.g. if Customer bean was under ejb/Customer in version 1, in version 2 it would be under ejb/Customer2</li> <li>Have a business facade in the application with a stable basic interface (Factory-style) which, when asked for Customer bean, tries to find the highest-versioned JNDI name (not on every call, of course, can cache for a hour or so). That facade could (and should) be deployed as a separate application -- and never or very rarely updated</li> <li>Now every new client would get access to the latest application deployed, and the applications won't conflict.</li> </ul> <p>This approach takes a careful planning and testing, but should work IMHO.</p> <p>I recently modified a few applications in a similar way to let them coexist in the same domain (before they used the same JNDI name for different data sources). </p>
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    1. POHot Deploy a Java EAR to Minimize or Eliminate Downtime of an Application on a Server?
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    1. USVladimir Dyuzhev
    1. USVladimir Dyuzhev
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      1. VTUpMod
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    1. COThat is helpful and a very straightforward and reasonable solution. Unfortunately, many of our clients do not have load balancers and the way our session state is saved is a bit jacked and saved only on the local app server's cache (I have been advocating for a change to that).Thanks for the input.
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      1. USIchorus
    2. COOh, so you're deploying your app on clients' servers? That changes a lot, of course. Unless you implement some kind of versioning in JNDI names, it's impossible, I'd say...
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      1. USVladimir Dyuzhev
 

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