Historically, sharing a Linux server entailed all kinds of untenable compromises. In addition to the security concerns, there was simply no good way to keep one application from hogging resources and messing with the others. The classic “noisy neighbor” problem made shared systems the bargain-basement slums of the Internet, suitable only for small or throwaway projects.
Serious use-cases traditionally demanded dedicated systems. Over the past decade virtualization (in conjunction with Moore’s law) has democratized the availability of what amount to dedicated systems, and the result is hundreds of thousands of websites and applications deployed into VPS or cloud instances. It’s a step in the right direction, but still has glaring flaws.
Most of these websites are just piles of code sitting on a server somewhere. How did that code got there? How can it can be scaled? Secured? Maintained? It’s anybody’s guess. There simply isn’t enough SysAdmin talent in the world to meet the demands of managing all these apps with anything close to best practices without a better model.
Containers are a whole new ballgame. Unlike VMs, you skip the overhead of running an entire OS for every application environment. There’s also no need to provision a whole new machine to have a place to deploy, meaning you can spin up or scale your application with orders of magnitude more speed and accuracy.