Serverless and FaaS

In the previous sections, we discussed various types of clouds, cloud service delivery models, and the core technologies that drove this technology revolution. Now that we have established the baselines, it is time to define the core concept of this book – serverless.

When we say serverless, what we are usually referring to is an application that's built on top of a serverless platform. Serverless started as a new cloud service delivery model where everything except the code is abstracted away from the application developer. This sounds like PaaS as there are no servers to manage and the application developer's responsibility is limited to writing the code. There are some overlaps, but there are a few distinctive differences between PaaS and serverless, as follows:

PaaS	Serverless
Always-on application	Runs on demand
Scaling requires configuration	Automatic scaling
More control over the development and deployment infrastructure	Very limited control over the development and deployment infrastructure
High chance of idle capacity	Full utilization and no idle time, as well as visibility to fine-tune and benchmark business logic
Billed for the entirety of the application's running time	Billed every time the business logic is executed

Table 1.1 – PaaS versus serverless

In the spectrum of cloud service delivery models, serverless can be placed between PaaS and SaaS.

FaaS and BaaS

The serverless model became popular in 2014 after AWS introduced a service called Lambda, which provides FaaS. Historically, other services could be considered ancestors of serverless, such as Google App Engine and iron.io. Lambda, in its initial days, allowed users to write functions in a selected set of language runtimes. This function could then be executed in response to a limited set of events or be scheduled to run at an interval, similar to a cronjob. It was also possible to invoke the function manually.

As we mentioned previously, Lambda was one of the first services in the category of FaaS and established itself as a standard. So, when we say serverless, people think of FaaS and, subsequently, Lambda. But FaaS is just one part of the puzzle – it serves as the computing component of serverless. As is often the case, compute is meaningless without data and a way to provide input and output. This is where a whole range of supporting services come into the picture. There are services in the category of API gateways, object stores, relational databases, NoSQL databases, communication buses, workflow management, authentication services, and more. In general, these services power the backend for serverless computing. These services can be categorized as Backend as a Service (BaaS). We will look at BaaS in the next chapter.

Before we get into the details of FaaS, let's review two architecture patterns that you should know about to understand serverless – the microservice architecture and the Event-Driven Architecture (EDA).