Problem:
No memory on the host. You can’t even reboot the host due to a lack of memory.

Solution:

Trigger OOM-killer by executing these commands:

echo 1 > /proc/sys/kernel/sysrq
echo f > /proc/sysrq-trigger
echo 0 > /proc/sys/kernel/sysrq

Yes, it’s bad, but sometimes you don’t have a choice…