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Hi,
When I first started to toy around with LVS, I did just what is written
here:
i tried to use the SH scheduler for "session affinity" at L7.
Looking at your original post from 2004, you are using source hashing with a
weight of 1. This will result in the service being overloaded when the
number
of connections is greater than 2, as your output of ipvsadm shows. Have you
tried increasing the weight?
No I haven't. Can you explain why a weight of 1 will result in the service
being overloaded, and how would weight = 2 make a difference?
As I understand it, the weight only specifies the relative weight of the real
servers. It has nothing to do with the actual number of connections. Am I
wrong? My current setup also has weight = 1 for all real servers.
The weight when used with SH and DH has a different meaning than most, if not
all, the other standard LVS scheduling methods. Although this doesn't appear
to be mentioned in the man page for ipvsadm.
From ip_vs_sh.c
The sh algorithm is to select server by the hash key of source IP
address. The pseudo code is as follows:
n <- servernode[src_ip];
if (n is dead) OR
(n is overloaded, such as n.conns>2*n.weight) then
return NULL;
return n;
That would explain the things I saw.
In the mean time, I went back to a configuration with the SH scheduler
and a weight for both real servers of 200, and things seem to run fine.
Thank you for the advice!
Best regards,
Martijn Grendelman
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