Virtual Machines
Hypervisors, guest operating systems and virtual hardware; the lifecycle from provision to terminate; patching as an operational obligation; immutable images versus machines you log into; and one large VM against several small ones.
A rented machine is a slice of someone else's machine: a guest operating system on virtual hardware, held apart from every other tenant by a hypervisor. You get a complete OS and the strongest ordinary isolation boundary on offer, and you inherit every obligation of running one.
Q · What am I actually getting when I rent a machine that is not a machine, and what do I owe in return?
The hypervisor is the component that divides one physical machine between strangers. Understanding what it multiplexes explains both why a VM boundary is stronger than a container's and why your latency can double while your CPU graph stays flat.
Q · Who divides one physical machine among many tenants, and what does sharing that machine cost me?
Provision, boot, configure, run, patch, restart, terminate. Each state has a characteristic way of failing, a signal that reveals it and usually a signal that reassures you while it happens — and the two states teams skip planning for are patch and terminate.
Q · What states does a virtual machine pass through from request to destruction, and how would I notice when it fails in each of them?
Either you log into machines and change them, or you build an image and replace them. The first is faster today and produces servers nobody can reproduce; the second costs a build pipeline and pays for itself the first time you have to scale out or recover in a hurry.
Q · Should I fix a running server or replace it, and when does the difference actually matter?
Vertical scaling is one instruction and no new concepts, right up to the instance size that does not exist. Horizontal scaling removes the ceiling and the single failure domain, and charges you statelessness, a load balancer, and a fleet to keep identical.
Q · Should this workload run on one large virtual machine or several smaller ones, and what does each choice cost me?