Hi Malcolm, On Tue, Mar 04, 2014 at 08:43:47PM +0000, Malcolm Turnbull wrote: > Willy, > > Exactly right, but it is a common misunderstanding. > > Out of interest, How hard would it be to get a least connection > scheduler to take account of cumulated connections?
It also uses them slightly because it takes care of doing some round robin when all values are equal. > It would/might make it far more useful for HTTP.. Off the top of my > head I think least conns in LVS is based on cummulative for 60 > seconds (which again causes a lot of confusion).... > > Just had a quick look here: > http://www.austintek.com/LVS/LVS-HOWTO/HOWTO/LVS-HOWTO.ipvsadm.html > and to calculate active conns for LC: > active connections = ActConn * K + InActConn > Where K is between 32 and 50? It's different here. Don't forget that LVS runs at the packet level and that for this reason it needs to consider recently closed sessions to avoid reusing too fast some ip+port combinations, or to overflow a server's TIME_WAIT table. Here we don't have this problem. > So probably way more confusing and yet most of our customers prefer > the LeastConnection handling for HTTP in LVS rather than HAProxy.... Leastconn in LVS is used as a trick to get more or less the maxconn feature we have in haproxy, because you're sure that you won't overflow a server before all the farm is full. So this is a different usage. > I also slightly think that they just instinctively like the bigger > numbers for connection count ;-). > http://blog.loadbalancer.org/look-why-cant-you-just-tell-me-how-many-people-are-connected-to-the-load-balancer/ Yes but again, it's the never-ending L4 vs L7 comparison where on L4 you *have* to consider TIME_WAIT and all half-closed connections while you don't need to take them into account in L7. > Just thinking the new keepalive functionality will probably effect this as > well? Slightly but not completely. At the moment, and idle keep-alive connection is not accounted for on the server side, which means that we could very well add a new connection to that server. However, what generally counts with nowadays servers is the number of connections being served. For example, an idle connection kept with Nginx will not hurt it at all. And using leastconn even with static objects will make sense because it will try to balance the number of active transfers. This makes sense from a bandwidth and CPU usage point of view. Cheers, Willy
