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From "Shapira, Yoav" <Yoav.Shap...@mpi.com>
Subject RE: Howto deploy a new version of my webapp without disturbing the customer?
Date Fri, 01 Oct 2004 12:52:25 GMT

Hi,

>You are really lucky not to offer your service to thousands of
>customers. From what I can see in the sales figures, those customers
>never sleep! And so do the product managers: the best downtime is no
>downtime :-) Thus I want to keep the version cycle as small as
>possible.

Yes, it's true that customers/users never sleep.

I want to offer an alternative approach here.  This scenario is one that
I had in mind when contributing the balancer app to Tomcat.  Using the
balancer app to address this issue can result in zero down time.  Here's
the setup:

Initial:
- Tomcat server 1 with your app v1.0
- Tomcat server 2 with your app v1.0 turned off
- Tomcat front-end running only balancer (so this is a tiny, fast,
Tomcat installation consuming almost no resources), which redirects
requests for your app to Tomcat server 1.

Now v1.1 of your app is ready, here's what you do:
- Turn on Tomcat server 2, which has your app v1.0 still
- Modify the balancer rules to redirect requests for your app to Tomcat
server 2
- Update server 1 (you can turn if off, restart it, do whatever you
need, as your users aren't using it now) with your app v1.1
- When it's ready, modify the balancer rules again to that requests for
your app go to Tomcat server 1.
- Watch things for a while, and if something goes bad with your new app
you can just modify the balancer rules so that users go back to 1.0
(again, no down time!)
- But if things go well, you can turn off and update server 2 as well so
that you're ready for the next round.

This is just the standard cluster/traffic-director setup done with
Tomcat's balancer, which makes is a 100% Java, 100% free, lightweight
solution.  There are non-Java and/or $$$ alternatives to this same
approach that also work well.

The focus is on using multiple servers instead of one, thereby allowing
you to modify any one server at a time without causing down time for
your users.

Yoav



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