We had quite strange scenario. Two hosts with sidekiq, one working well, second one gets stuck after few seconds or minutes. Happened in workers with opening new TCP/UDP connections. So, I started to review all the files, where ‘max files’ is set.

$ cat /etc/security/limits.conf
* soft nofile 30000
* hard nofile 60000

tom@web:~$ ulimit -Hn
60000
tom@web:~$ ulimit -Sn
30000

tom@web:~$ /sbin/sysctl -a | grep "file-max"
fs.file-max = 60000

So, all this looks OK so far. After numerous checks I’ve found, that our eye  process is running for a while, maybe since the beginning and probably it took old file-max  settings. How to check? Simply run eye info  or get PID of the sidekiq  process and run following command (assume 22613 is the PID):

tom@web:~$ cat /proc/22613/limits
Limit                     Soft Limit           Hard Limit           Units
Max cpu time              unlimited            unlimited            seconds
Max file size             unlimited            unlimited            bytes
Max data size             unlimited            unlimited            bytes
Max stack size            8388608              unlimited            bytes
Max core file size        0                    unlimited            bytes
Max resident set          unlimited            unlimited            bytes
Max processes             516140               516140               processes
Max open files            1024                 4096                 files
Max locked memory         65536                65536                bytes
Max address space         unlimited            unlimited            bytes
Max file locks            unlimited            unlimited            locks
Max pending signals       516140               516140               signals
Max msgqueue size         819200               819200               bytes
Max nice priority         0                    0
Max realtime priority     0                    0
Max realtime timeout      unlimited            unlimited            us

Gotcha! 1024 as soft-limit, 4096 hard limit. The fix is pretty simple – just quit eye , load it’s config and restart sidekiq.

tom@web:~$ eye quit
quit...

tom@web:~$ eye load config.eye
eye started!
config loaded!

tom@web~$ eye restart sidekiq

tom@web:~$ cat /proc/4624/limits
Limit                     Soft Limit           Hard Limit           Units
Max cpu time              unlimited            unlimited            seconds
Max file size             unlimited            unlimited            bytes
Max data size             unlimited            unlimited            bytes
Max stack size            8388608              unlimited            bytes
Max core file size        0                    unlimited            bytes
Max resident set          unlimited            unlimited            bytes
Max processes             516140               516140               processes
Max open files            30000                60000                files
Max locked memory         65536                65536                bytes
Max address space         unlimited            unlimited            bytes
Max file locks            unlimited            unlimited            locks
Max pending signals       516140               516140               signals
Max msgqueue size         819200               819200               bytes
Max nice priority         0                    0
Max realtime priority     0                    0
Max realtime timeout      unlimited            unlimited            us

voila! We’re back on track :)