Web Development with Node and Express Chapter 21 - Going Live

• Cloud hosting is also highly virtualized. That is, the server(s) your app is running on are not usually physical machines, but virtual machines running on physical servers. This idea was not introduced by cloud hosting, but it has become synonymous with it.

• SaaS(Software as a Service): SaaS generally describes software (websites, apps) that are provided to you: you just use them. An example would be Google Documents or Dropbox.

• PaaS(Platform as a Service): PaaS provides all of the infrastructure for you (operating systems, networking—all of that is handled). All you have to do is write your applications. While there is often a blurry line between PaaS and IaaS (and you will often find yourself straddling that line as a developer), this is generally the service model we’re discussing in this book. If you’re running a website or web service, PaaS is probably what you’re looking for.

• IaaS(Infrastructure as a Service): IaaS gives you the most flexibility, but at cost. All you get are virtual machines and a basic network connecting them. You are then responsible for installing and main‐ taining operating systems, databases, and network policies. Unless you need this level of control over your environment, you will generally want to stick with PaaS. (Note that PaaS does allow you to have control over the choice of operating systems and network configuration: you just don’t have to do it yourself.)