Upgrading the kernel to "combat" servers?

Question

linux

Hello gentlemen, I am a beginner Linuxoid and this question practically does not let me sleep - very interesting.
How does (if it does) update the kernel on "combat" servers, somewhere in the data center of a hosting company that guarantees 99.9% uptime. After all, without rebooting the machine, as far as I understand, you can’t switch to a new kernel? So the kernel is not updated? And how then does the closing of holes occur, which are found over time in the nucleus? Maybe there is something to read on this topic, and on the topic of highly loaded systems in general (in particular, the theory of working with them is more interesting) or is it from the category of secrets?

Answer 1

Why is it not updated? I update the kernel once a year or six months and do a reboot, well, or if there is some kind of terrible vulnerability, then at the first opportunity, at night ... fortunately, there are no problems in debian / ubuntu with this.

Answer 2

Either the aforementioned ksplice (but it doesn't always work) or the keyword is HA cluster. We update the nodes in turn, without interrupting the service.