Cloud Application Reference Architecture: Types & Descriptions

Instructor: Giorgos-Nektarios Panayotidis

George-Nektarios has worked as a tutor and student consultant for five years and has a 4-year university degree in Applied Informatics.

There are two different options for a Cloud application architecture: the traditional 3-tier one and the modern Service-Oriented one. This lesson will analyze the distinct characteristics of these options and differences between them.

Tightly or Loosely Coupled?

Imagine you own a car company. You've got several choices to make. Do you want to make a race car built for a single purpose, or do you want to make a versatile car with mass appeal that will sell like hotcakes? Choosing how you build a car depends on the type of car you want to make and the goals and constraints associated with making it.

For example, if you're building the race car, you'll want all of your components to be customized so they work together in the best way possible. Doing this will result in high performance, but also in higher cost as you will need to pay someone to make those parts specifically for you. On the other hand, if you're building a mass-market car, you can choose parts that will be easily replaceable and interchangeable with other cars. Manufacturers will have developed standard parts to increase their usability, and you can take advantage of this to build more cars at a quicker pace and lower cost.

Similarly, while developing the architecture for cloud applications, you'll want to consider various factors depending on the type of application you're developing. You can choose to design an architecture with tightly-coupled components, which would be akin to the race car, or you can choose an architecture with loosely-coupled components, akin to the mass-market car. Coupling is one of the major differentiating characteristics between cloud architectures. In this lesson, we'll delve into the details of two reference architectures: 3-Tier Architecture (3TA), which is tightly-coupled, and Service Oriented Architecture (SOA), which is loosely coupled.

3-Tier Architecture

3-Tier Architecture (3TA) is the traditional reference model, when it comes to web-based applications. This model, as its name suggests, consists of three tiers/layers:

  1. Presentation tier is the application's front-end or Graphical User Interface (GUI), where the client computer performs certain operations. In 3TA, the presentation layer is closely connected to the other two tiers, which are seen as server layers in the context of client-server architecture.
  2. Business/logic tier is the middle layer where all the processing is carried out; it is the app's logic. It is the intermediary layer between the data and presentation ones and fetches the resources requested by the latter from the former.
  3. Data tier is the lowest layer, in which the storage and retrieval of information is performed within databases or other organized files.

An additional noteworthy element with regard to 3TA is that all the tiers are independent from one another from a coding standpoint; therefore, the data tier, for example, cannot contain logic or presentation code. Thus, code maintenance is more easily performed. Also, the code modules are tightly coupled, in that they are highly interdependent. These modules are routines, subroutines and scripts which invoke one another and, consequently, the change in one module very often implies a requirement for changes in the other parts.

Service-Oriented Architecture

Service-Oriented Architecture (SOA) is another type of architecture, which was born in the early 2000s and began to be promoted along with cloud computing. In fact, SOA is considered to be one of the fundamental technologies which cloud computing took advantage of and was built upon. SOA is built on services which are often defined as loosely-coupled programs acting on behalf of others (or the user) to carry out a specific goal. Each of these programs provides a particular basic business/logic functionality, which is complementary to a multitude of other functionalities. Each of the possible functionality combinations corresponds to a broader goal. Now, in practice, services may implement integration, business/logic, or access-to-data functionalities. A frequently used real-world example of SOA is an online storefront, which can be a combination of several services. A storefront typically contains a user interface service and three web application services: one for the inventory (warehouse info), one for the customer info, and for shipping (product delivery). Please note that these services may be further divided into lower-level ones.

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