Overnight out of the blue with no changes to our Zabbix proxy it failed and tried to restart. 

I had a look at the logs and it reported the following error message constantly:

zabbix_proxy [31839]: failed to fork: [12] Cannot allocate memory

After 24 hours downtime I am at a loss after trying the following:

• Rebooting Centos servers (Sever/Proxy)
• Upgraded Zabbix to 4.0.11
• Patched Centos servers
• Rebuilt two brand new proxies which had the exact same issue
• Recovered Proxy to yesterdays backup
• Disabled any loadable modules
• Updated Centos sysctl / limits.conf:

-bash-4.2$ ulimit -a
core file size (blocks, -c) 0
data seg size (kbytes, -d) unlimited
scheduling priority (-e) 0
file size (blocks, -f) unlimited
pending signals (-i) 31190
max locked memory (kbytes, -l) unlimited
max memory size (kbytes, -m) unlimited
open files (-n) 37767
pipe size (512 bytes, -p) 8
POSIX message queues (bytes, -q) 819200
real-time priority (-r) 0
stack size (kbytes, -s) 8192
cpu time (seconds, -t) unlimited
max user processes (-u) unlimited
virtual memory (kbytes, -v) unlimited
file locks (-x) unlimited

• Upgraded from 8GB to 16GB ram with 8GB reservered (now back to 8GB)

free -m
total used free shared buff/cache available
Mem: 7820 1007 3089 678 3724 5847
Swap: 3687 0 3687

Could this be this issue : https://support.zabbix.com/browse/ZBX-9084 ?

Please help me, and I am already in the process with my manager of putting together the case to obtain Enterprise support.

Cheers

James