THANK YOU! > > > work and I only say should because I personally haven't tried > storing > > > PHP session information on an NFS share before. There was some > recent > > > > Then how do you share your session data between more than one web > server? > > You have session data in a database? > > I don't need to. As described below, my load balancing device sends each > session to the same machine it was originally directed to based on > source IP. I believe LVS calls it the Persistent Port Solution > (http://www.linuxvirtualserver.org/docs/persistence.html). > > > > that IP as well. We use hardware layer4 switches in front of our > systems > > > to perform automatic load balancing, health detection and failover. > The > > > particular devices we use can maintain user session to one machine > or > > > the other, negating the need to store the PHP session information on > the > > > NFS box. This is essentially filling the role of the LVS and allows > us > > > to provide very high service availability. > > > > Wow, must be nice to have that kind of money. :) How does a _switch_ > > know > > how to maintain session data for the _application_ layer in _front_ of > a > > web > > server?? Sounds nice anyway. :) > > They're intelligent switches. The ones we use are strictly layer 4 > meaning we can perform intelligent actions based on source IP, source > port, dest IP, dest port and protocol (TCP/UDP). There are others that > look at layer 7 meaning I could redirect to different machines based on > actual content in the request like a cookie for example. We've used > Alteon (now Nortel) and Foundry switches for years for this purpose (and > others). They really do make load balancing a breeze and can work with > high traffic loads. We're currently load balancing >4000 HTTP > requests/sec and ~180 mbit/sec through one of them (not SM ;) ). We also > use them for SMTP, POP and IMAP load balancing. This might sound like a > sales pitch but it's not. ;) It looks like you can do some of the same > things with LVS which didn't exist when we started our projects. > > > > As far as using Perdition, it wasn't really designed to be a load > > > balancer, at least when I last used it and wouldn't really be > effective > > > at it. Your load balancing would be determined by WHO was logging in > at > > > a particular time instead of how loaded a machine was. If all the > users > > > assigned to server 1 were logged in an none assigned to server 2 > you'd > > > have one box loaded and one completely idle. I would suggest that if > you > > > > Wow, OK, thanks for clarifying. Hadn't really read up on it yet, but > will > > certainly do so given what you say here. > > Sure. Perdition is _extremely_ useful for those who need its > functionality. We wouldn't have been able to easily move 36,000 email > accounts from an old VMS machine to our current email system without it. > Using perdition, none of the users had to change any of their mail > server settings as everything 'just worked'. > > > > get to the point where DNS load balancing isn't sufficient for your > > > needs you take the plunge and set up a Linux load balancer or > purchase a > > > hardware switch that'll do it for you. Life is much easier that way > =) > > > If you scale even further, separate your IMAP/SMTP/HTTP servers. If > you > > > do that, you can grow the specific service that's being utilized the > > > most without having to rebuild all services for each machine. By > that > > > time you should be bringing in enough money that cost wouldn't be > > > prohibitive. > > > > Yeah, that's the first thing on our list once we take the next step, > so > > I'm > > glad to hear someone reaffirm it. Don't really like IMAP/SMTP/HTTP on > the > > same server but we're stuck there for now. One possibility given the > > other > > response today is that maybe it's OK to run just one IMAP server on > our > > NFS > > machine where the mail spool is. Our front-end HTTP/SMTP servers > would > > reduce their load a bit, as long as we don't kill the NFS server.... > > I personally think you should stick with two of everything you can. If > you have one IMAP server and it dies then your entire mail system is > dead from your customers' perspective. It doesn't matter if SMTP and > HTTP are working, they still can't get their mail. You're making them > even more dependent on your mail system because if they're using SM as > their primary e-mail client, the only way they can see any of their > e-mail is if your system is up. With a desktop client using POP at least > they could see historical e-mails. In a case like this, redundancy is > the mantra. You don't want to appear to have unreliable services. It's > also highly unlikely you'll kill your NFS server. NFS processing is > almost entirely disk and bandwidth. Even with 36,000 accounts we barely > push either. Not everyone logs in at the same time so we generally see > 3-4 mbit/s peak with the average more like 500 kb/s.
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