> -----Original Message----- > From: Andre-John Mas [mailto:aj...@sympatico.ca] > Sent: Tuesday, August 25, 2009 6:30 PM > To: Tomcat Users List > Subject: Multiple data centers and redundency? > > Hi, > > I have been asked to look into a solution that would involve a few > different data centres each with their own set of load balanced Tomcat > servers. The requirement is for the users not to lose their session if > one data center goes down. I have never had to work on something this > large and have no idea to what extent this can be achieved with Tomcat. > > My initial thoughts would be for each data center to have a session > pool, which is synced with each other, so if ever a Tomcat server or > data center goes down they can check in the pool to see if it exists > and then reuse that. It would mean extra communication behind the > scene, but I see no other way go about it. > > Any help would be appreciated. > > André-John
Has anyone really done any math to determine the risk? Here an example of what I mean. Say you are in a high quality co-location. The probability of an outage is maybe once in 3 years. That's overstating the probability in my mind, but we'll use it. Let's also say that you have a high quality clustering solution in place in each data center that handles failover of any equipment WITHIN the data center. Say the average length of a user/customer session is 2 hours, and your failover system will route any new users to a remaining data center. I think 2 hours is kind of a long session but we'll use it. Say you have two data centers. So, the probability of an average customer being affected by a data center outage is: 1/( (2 hours)/24(Hours day) * 1/(3*365))/2 (Data centers) The probability of an average customer being affected by an outage is conservatively 1 in 26280. Expressed as a percentage, the probability of any individual session being affected is 0.0038%. Is your application really so big and critical that you have to address this very small percentage chance of a session being interrupted? George Sexton MH Software, Inc. http://www.mhsoftware.com/ Voice: 303 438 9585 --------------------------------------------------------------------- To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org
