Schedule: No dest found

Martijn Grendelman martijn at grendelman.net
Wed Apr 14 13:46:08 BST 2004


Hi,

Every once in a while, my director denies connections on the VIP, even
though both real servers are up. After a short while (seconds, up to a
minute or so) everything turns back to normal. I think (but I am not 100%
sure) that while one client gets a connection refused, another client can
connect just fine. I have received complaints from users, while at that
time, everything seemed fine from my end. At other times, I experienced
the problem myself. Also, at times, the response from the web servers is
slow, when accessed via the VIP, while the response on the real servers
directly is fast, as it should be.

I use LVS/DR on Linux kernel 2.4.25, with the sh (source hashing)
scheduler. Statistics show that both real servers are being accessed more
or less equally, as could be expected with source hashing.Today, I turned
on IPVS debugging in the kernel and set the debug level to 3. 'dmesg' now
says "IPVS: Schedule: no dest found.", repeatedly. Maybe someone on the
development team can explain this? In what situations should IPVS log that
message? What's going wrong here? Please note that this is _not_ a problem
with the real servers. At the times connections are denied at the VIP, the
Apache servers respond on their RIPs just fine.

I hope someone can shed some light on this, because it's becoming more and
more of a problem and I am considering turning off the LVS completely.

In response to a message about this problem I sent to the list on March
8th, someone said that he experienced the same problem, but it went away
after he switched to RR scheduling. I wish I could do that too, but I
don't have any secure way to share HTTP sessions between the real
servers...

Best regards,
Martijn.



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