Few days ago I've installed new server on Ubuntu 12.04 and migrated all my data and services to it from an old one (pretty outdated 2011 year server). There are many different services installed on it: nginx, mysql, memcached, varnish, etc.
Now I have an issue with network connections: limited amount of connections works normally but other would not, they just time out. Such requests are not visible in web server's access log at all. Moreover, some outgoing requests with cURL are not working too, they time out at 30 second. Sometimes I cannot connect to the server -- SSH connections timeout sometimes too! Pinging google:
--- google.com ping statistics --- 33 packets transmitted, 0 received, 100% packet loss, time 32017ms
I have not updated or installed any additional firewall nor changed system network config options.
You can easily reproduce the problem by accessing any page (ex: http://en.advisor.travel/poi/Wroclaw_Palace-15356) and quickly refreshing the page multiple times. You'll end with "Server is not available" browser error.
It almost seems that the server has some weird network connections limit or rules to block quick connections succession from one IP but I cannot find any useful setting :/ Nothing interesting can be found in
/etc/sysctl.conf has everything commented out but default lines:
net.ipv6.conf.all.disable_ipv6 = 1 net.ipv6.conf.default.disable_ipv6 = 1 net.ipv6.conf.lo.disable_ipv6 = 1
ufw is stopped.
Any ideas what's happening and what to do are much appreciated!