UNIX for Advanced & Expert Users

I think I did answer the first but in a round-about way. It's not that leaving it down performs some function. It's that leaving it down keeps it out of the pool. So if the app is bad I don't start sending customer to it again.

The second question just go wrapped in with the first but my answer applies here as well. No it doesn't prevent me from debugging them. Just prevents me from returning a potentially bad server to the pool.

---------- Post updated at 03:37 PM ---------- Previous update was at 03:26 PM ----------

I agree with you on this. Where I work, however, "uptime" is measured as an SLA. So if I'm hosting a web service, we're not judged by the individual uptime of the hosts and services that make up a pool, we're judged by the availability of the service. So "Does the service respond with the proper data in < 1 sec" is far more important than "Did all the servers in the web service pool stay up this year".

If I restart apache (as an example) automatically, and there is something wrong with that instance that causes it to respond in 5 sec instead of <1, I'll have to answer for that.

So my general philosophy is that you provide high availability with hot spares, load balancing, or some other type of redundancy. Not with auto-restarts. But it sounds like I may be alone in this.

Are most people being measured by uptime on individual hosts/apps as opposed to service availability?

If a server going down doesn't break anything then I guess it's not quite as important. You never hinted about that until now though, many things aren't in pools like that. Presumably some servers are more important than others, too -- you can't avoid having some sort of physical storage somewhere...

Most of the servers I administer are behind a load balancer just like yours and they come out of a pool when they are acting up. However, what I tend to do (for tomcat applications for example) is get a thread dump of what the application is doing at the time, get all the logs, as well as what processes including memory/cpu usage are running on the system. I then use this to debug it. If this is a single point of failure I go for the quick restart after collecting as much data as possible.

Our uptime is managed by service availability, but our SLA's include hosts/services on those hosts. So I am required to respond to them even if the service is still functioning properly.