On 09/28/2011 04:47 AM, Alan Wright wrote: > Hi > > I am migrating from resin 2 to 4.0.22 and have a single host configured > with a web-loadbalance tier (1 server) and an application tier (3 servers). > > We have elected to do this for resilience and also to make adding hosts > at a later date easier to implement. > > We start 3 servers on the app-tier to create a "triad" but it may be > that we only really need 2 servers to get basic failover resilience. Is > there any benefit from having a triad or am i just wasting resources > with the overhead of loading the same application environment 3 times?
Three might be overkill in your configuration. Statistically, it would give you a better resilience. A main scenario for the triad was a customer case where they took down servers periodically for maintenance and had a crash at the same time (this was before the triad or the hub-and-spoke model and with an 8-server cluster), and therefore some of their persistent sessions were lost. The three server triad gives you a backup, even when you take down a triad server deliberately. I don't think that scenario applies in your case. Another main reason is failover load. On a fully-loaded system, taking down (or crashing) one of three servers means the other two work 50% harder. If there were only two, it would be 100% which could cause a cascading failure. That scenario doesn't apply because your backup servers are using the same CPU, so you shouldn't have a cascading failure. In your case, since you only have the extra servers for reliability, and they're on the same machine, the third server isn't as important. -- Scott > Also each of the app-tier servers is pointing at the same webapp > directory since they are all on the same host. Is this OK or is it > dangerous? > > > Additionally the application is started as root and for the app tier we > use<user> and<group> to change the user. When we try to do the same > thing in the web-loadbalancer tier the application fails to start. Is > this normal/to be expected? Is it safe for the web-tier to be running as > root? > > > Thanks to those who have responded to my earlier queries. > > Alan > > _______________________________________________ resin-interest mailing list [email protected] http://maillist.caucho.com/mailman/listinfo/resin-interest
