Cloud computing or all kinds of *aaS

Initially, I wanted to write a post about Serverless. I've started researching and found out that my understanding of Serverless is not clear, at least in terms. The biggest discovery for me was that Serverless and Cloud are not interchangeable words. Therefore I've decided to make a quick overview of existing approaches before diving into one of them.

We will start with the Big Three of cloud service models: IaaS, PaaS, SaaS, i.e., Infrastructure as a Service, Platform as a service, and Software as a service. Big companies like Amazon, Microsoft, Google cover all of them. Google Cloud is IaaS, Google App Engine is PaaS, Google Drive and other services for end-users are SaaS.

IaaS provides users with hardware — servers, storage, network as an on-demand service. It gives a lot of flexibility, but at the same time, it requires users to install and configure needed software on their own.

PaaS offers an infrastructure, OS, middleware, database management + some additional software to develop and deploy applications. Probably, you've used Heroku to host your website for free. It's one of the first platforms of this kind. Another good example is Google App Engine. It is a product that provides Web app developers and enterprises with access to Google's scalable hosting and Internet service. The App Engine has limited language support. You're allowed to store data only in Google Cloud Storage services and use the Google query language. We are losing flexibility...huh?

SaaS is a way of delivering applications over the Internet—as a service. Instead of installing and maintaining software, you simply access it via the Internet, freeing yourself from complex software and hardware management. Google Drive, DropBox, Zoom, all kinds of CRM/ERP solutions, you name it.

Before the Serverless the most effective way to build SaaS applications was to develop microservices, deploy them on a Platform as a Service and let the PaaS manage a lot of things. Serverless is just another degree of automation that lies between PaaS and SaaS. It usually includes two concepts: Backend as a Service (BaaS) and Functions as a Service (FaaS).

BaaS makes your app a "rich client." You are not building REST-APIs anymore. Now your client application talks to the database directly with an authentication layer in front of the database. Google has a Firebase platform, and Amazon has Amplify with Cognito for authentication purposes.

With FaaS you're still able to build REST API, but, unlike traditional architectures, server-side logic consists of independent functions that run in stateless containers that are event-triggered, ephemeral (may only last for one invocation), and fully managed by a third party. AWS Lambda is one of the most popular implementations of a Functions-as-a-Service platform.

You can use just one of them or both at the same time. For example, you're building a chat app with Firebase (BaaS), and you want to send a push notification to users that receive the message. You add this message to your database on the client, and this event triggers a cloud function (FaaS) responsible for sending push notifications to specified users.

There are two big benefits when using one of these as-a-service models:
- Faster time to market. You don't need to reinvent the wheel and manage it.
- Resources sharing lowers costs. In some cases, you may even have free monthly/weekly quotas.

The main drawbacks are:
- Vendor Dependency. You're playing by their rules now.
- It may be hard to integrate with existing infrastructure.
- You may face security issues.

If something is not clear, look at the pictures below.

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