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Dear Falko
On 23/10/14 09:06, Falko Koenig wrote:
127.0.0.1:8000 timed out (110: Connection timed out) while in http auth
state, client: XXX.XXX.XXX.XXX, server: 0.0.0.0:993, login: “USERNAME”
2014/10/22 17:16:52 [error] 2073#0: *4393196 auth http server
127.0.0.1:8000 timed out (110: Connection timed out) while in http auth
state, client: XXX.XXX.XXX.XXX, server: 0.0.0.0:995, login: “USERNAME”Because of that it isn’t possible that the answer of the LDAP server is
sent too slowly back to the nginx. The servers are in a cluster
configuration and one server processes 20.000 Connections. Are there any
required kernel parameters for solving the problem?
My random guess.
Linux has a maximum of open connections.
You can get the number by the following command:
sysctl net.ipv4.ip_local_port_range
net.ipv4.ip_local_port_range = 32768 61000
The default on my host are 28232 local ports. For each connection a
local port is used. Because IMAP/POP3 are persistent connections, the
local ports are getting rare on your system.
You can increase this setting by /etc/sysctl.conf [1][2].
I guess your Perl script is a small CGI server running on localhost on
port XYZ (something like port 9000). This will add up additional local
port usages for every LDAP lookup. If you have 20’000 current
connection, 8000 used ports that are not yet been freed by the network
stack (see notes in [1]) and 2000 concurrent LDAP Perl request you’ll
reach the default limit of 28232 possible ports.
If your Perl script running on localhost I would recommend switching to
a Unix socket to save up additional local ports.
The Linux network stack (=> limitation of the IPv4 protocol) is not
capable of handling more than 65536 open connections [3].
An alternative to this problem might be a switch of a *BSD operating
system. Whatsapp is handling more than 2 million connections per host
with FreeBSD [4]. Or use a load balancer with multiple nodes.
Regards
Dominic
[1] Linux Network Tuning for 2013 – Nate Wiger vs Software
[2] http://dak1n1.com/blog/12-nginx-performance-tuning
[3]
Is there a hard limit of 65536 open TCP connections per IP address on linux? - Super User
[4] http://blog.whatsapp.com/196/1-million-is-so-2011