The good news is that Canonical has recently released its Livepatch service to apply critical kernel patches to Ubuntu 14.04 LTS, 16.04 LTS, 18.04 LTS, and Ubuntu 20.04 LTS without the need for a later reboot. Yes, you read that right: with Livepatch, you don’t need to restart your Ubuntu server in order for the security patches to take effect.
All Ubuntu personal users can link up to 3 different machines to Livepatch through the use of a token.
See How to Install Kernel Updates On Ubuntu without Rebooting
Canonical has recently released its Livepatch service to apply critical security kernel patches to the Ubuntu server without the need for a later reboot.