I also setup leastconn on stateless web application servers. So "the fastest" answers.
Baptiste On Thu, Mar 6, 2014 at 8:24 AM, Willy Tarreau <w...@1wt.eu> wrote: > 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 > >
