We have written previously about the outsourcing of the web stack. In this post, we will add more color on why the outsourcing of the entire web platform makes sense. While developers have gravitated en masse to offerings like Heroku, there is still a wider lack of appreciation for why PaaS is a major trend.

In this post, we are going to set aside the wider question of the economics of running your application on a PaaS versus hosting and maintaining your own servers. Our aim is to describe what constitutes a PaaS and how it differs from IaaS (such as Amazon Web Services) and other SaaS offerings like Salesforce.com.

The Four Pillars of a PaaS

1. No installation required. Whether your application is written in Ruby on Rails, Python, Java or any other language de jour there should be no need to install an execution environment when deploying your application to a PaaS. Your code should run on the platform’s built-in execution engine. While minor constraints are necessary, our view is that the successful PaaS providers will largely conform to the language specifications as they are in the wild. This ensures portability of your application between platforms and other hosted environments.
2. Automated deployment. A single click or command line instruction is all that stands between the developer and a live application.
3. Elimination of middle-ware configuration. Tweaking settings in Apache or Nginx, managing the memory on your MySql instance, and installing three flavors of monitoring software are now in the past.
4. Automated provisioning of virtual machines. Application scaling should happen behind the scenes. At 3am. Without breaking a sweat.

There are a few other characteristics of the new breed of PaaS services which we would regard as optional components of a platform but which greatly enhance its utility. By integrating other components into the web stack and constraining these to a few, well-curated and proven bundles, a PaaS offering can both consolidate services into a single bill but, perhaps more importantly from a developer’s point of view, ensure inter-operability and maintain a best-of-breed library. Heroku has done a great job of facilitating easy deployment of application add-ons such as log file management, error tracking, and performance monitoring.

There is often confusion as to the difference between PaaS and SaaS: a PaaS offering is an outsourced application stack sold to developers. A SaaS offering is a business application typically sold to business users.

The difference between PaaS and IaaS is more subtle and over time the dividing line is likely to blur. Today, the PaaS platforms begin where the IaaS services leave off: IaaS effects the outsourcing of the hardware components of the web stack. PaaS platforms effect the outsourcing of the middleware components of the web stack. It is the abstraction of the repetitive middleware configuration that has caught the imagination of developers. PaaS saves time and expedites deployments.