optimizing apache for high traffic

Why would you have keepalive's off? That is generally a huge performance benefit. Without seeing a more information, I don't think anyone could tell you why your site goes offline or how to tune Apache for your load.

robert

KeepAlives significantly hurt performance. They save some bandwidth and reduce average response times a bit, at the cost of a huge increase in memory consumption. That in turn significantly reduces the number of simultaneous clients that can be served.

Apache can be configured in such a manner that the memory load from keepalives isn't so huge (things like switching from mod_php to a fastcgi approach), but generally they're not worth it unless you have a ton of RAM. And that's not something that tends to happen in a VPS environment.

Yes, I took the advice from the Linode team and turned KeepAlives off. It does improve the site performance in my case.

Would it be helpful if I attach my htop/iotop or other results?

Further thoughts–Caching--

APC? (Pre 2.4 you have to tack it on, post you're g2g)

Memcache?

CDN? CloudFlare?

Where's your Database in all of this? Mysql are you running a performance profiler for helpful tuning?

Just some thoughts.