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Hi all,
I'm running a small apache cluster (2 loadbalancers in active-passive setup, 2
realservers serving HTTP and HTTPS).
All machines are Dell PowerEdge (R200 and R410 series), not older than 2 years,
running Ubuntu 11.04 with all packages updated.
My loadbalancers are configured with:
Heartbeat 3.0.4
Linux Director v1.186-ha
ipvsadm v1.25 2008/5/15 (compiled with popt and IPVS v1.2.1)
==== ldirectord.cf ====
checktimeout=10
checkinterval=2
autoreload=no
logfile="local0"
quiescent=no
virtual=x.y.z.141:80
real=x.y.z.135:80 gate 50
real=x.y.z.136:80 gate 50
fallback=127.0.0.1:80 gate
service=http
request="ldirector.html"
receive="Test Page"
scheduler=wrr
protocol=tcp
checktype=negotiate
virtual=x.y.z.141:443
real=x.y.z.135:443 gate 50
real=x.y.z.136:443 gate 50
fallback=127.0.0.1:80 gate
service=https
request="ldirector.html"
receive="Test Page"
scheduler=wrr
protocol=tcp
checktype=negotiate
==== ipvsadm -ln ====
IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
-> RemoteAddress:Port Forward Weight ActiveConn InActConn
TCP x.y.z.141:80 wrr
-> x.y.z.135:80 Route 50 110 51
-> x.y.z.136:80 Route 50 103 59
TCP x.y.z.141:443 wrr
-> x.y.z.135:443 Route 50 12 14
-> x.y.z.136:443 Route 50 12 6
==== the problem ====
When I (re)start my loadbalancer, the load is evenly balanced over my two
realservers. The output of ipvsadm -ln is at that moment comparable to the
output above. This is all as I would expert. Then, after somewhere between 30
minutes and 2 hours, the results of ipvsadm -ln changes to something like this,
while the load on the webservers does not significantly change:
IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
-> RemoteAddress:Port Forward Weight ActiveConn InActConn
TCP x.y.z.141:80 wrr
-> x.y.z.135:80 Route 50 0 1
-> x.y.z.136:80 Route 50 1 1
TCP x.y.z.141:443 wrr
-> x.y.z.135:443 Route 50 2 1
-> x.y.z.136:443 Route 50 1 0
Around the same time, the loadbalancer seems to become unbalanced, sending all
requests to one server. This is not always the same server, it seems to be
random. This server then becomes heavily loaded, while the other server is
idling. After a while (perhaps 30 minutes) the loadbalancer starts to send
packages to the unused realserver again. A little while after that, the balance
tips again, often preferring the other server this time.
The problem is always solved by restarting heartbeat, at which time the other
loadbalancer takes over and starts to distribute the load evenly again. Then,
after a while, this server starts to display the same issue.
A source for my problem might be found when running ipvsadm -ln --stats, which
displays the following:
IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Conns InPkts OutPkts InBytes OutBytes
-> RemoteAddress:Port
TCP x.y.z.141:80 20899 198954 0 21196756 0
-> x.y.z.135:80 10449 101877 0 10743318 0
-> x.y.z.136:80 10450 97077 0 10453438 0
TCP x.y.z.141:443 2852 46171 0 8971996 0
-> x.y.z.135:443 1426 23411 0 4485847 0
-> x.y.z.136:443 1426 22760 0 4486149 0
This would suggest that the number of connections are still evenly distributed
over the two realservers, even if the realservers themselves don't agree.
Can anyone help me locate the reason for the round robin scheduler not
distributing my requests evenly?
Thanks in advance,
Luc van Donkersgoed
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