We are in the era of transformative technology with several innovations springing up to improve service delivery and enhance customers’ satisfaction. More so is the introduction of microservices and other distributed systems into the software industry to revolutionize enterprise application development.

Its introduction has helped to solve problems associated with the age-long monolithic software development approach, overcoming its cons and achieving scalability.

In this article, I hope to dive deep into what microservices entail and highlight its significant use cases. Also, I will dive deep into the SOLID principles and other best practices necessary to build efficient microservices. With that, let's get started.

First of all, what is a microservice?

What is a Microservice?

This is a type of system architecture in which an application gets structured as a confluence of several independent, loosely coupled independent services. This ensures that each aspect of the overall application gets managed individually and still functions irrespective of the current state of other independent services. These independent servers still allow for information sharing over a given network.

It actively mirrors the distributed system model which segregates the various computers on a network and shares resources amongst them. The adoption of this model by big enterprises has been seen to be advantageous as it has greatly reduced server downtime, minimized costs and maintained efficiency.

The microservice system architecture also provides an upper hand to these firms as it rapidly provides scaling opportunities in case of a spike in user visits. The scaling could either be horizontal which involves activating multiple servers to handle user requests or vertical which involves increasing the CPU power of the server to efficiently handle user requests.

Unlike conventional monolithic systems, microservice best practices deviate slightly from the conventional ACID principles designed for related databases. Hence it's important to learn about best practices and principles which serve as a basis for building resilient microservices.

This will take us into the world of the SOLID principles. The solid principles form the general basis of object-oriented programming and design but have been adapted in the context of building resilient microservices. But what does SOLID represent?

Single Responsibility Principle
Open-Close Principle
Liskov Substitution Principle
Interface Segregation Principle
Dependency Inversion Principle

Let's discuss these in detail.

Single Responsibility Principle

This principle states that each service in the grand microservice architecture is responsible for a single functionality or possesses a single reason to change. This implies that the service in question is solely and wholly built to fulfil a specific application functionality and it is done cohesively.

This feature provides it with the liberty to scale bigger to effectively deliver on that given functionality. This forms the baseline for microservices development as it reduces the interference of several services due to service interdependency which is a side effect of monolithic applications.

Open-Close Principle

This principle was initially applied for object-oriented programming but is now also adapted for microservices development. It entails that services created within the overall microservice architecture are open to extension with additional service functionalities and communication via the services interface but should be closed to code modification.

This principle is necessary as code modification affects service functionality and stability and also serves as a risk for introducing bugs to the existing code which can ultimately cause errors in system function.

To ensure this, features such as code versioning allow for newer versions of an existing service to be created and deployed without affecting the older versions' functionality and maintain the system's efficiency. Also ensuring the implementation of APIs on each service and the concept of dependency inversion (which will be discussed in the subsequent section) helps to achieve this principle.

Liskov Substitution Principle

This principle is named after its originator, Barbara Liskov. It means that services built within complex microservice architecture can and should be easily substituted or replaced with no or minimal side effects to the entire microservice architecture. This feature also enables developers to build modular microservices applications.

It also enables the execution of the dependency inversion principle which will be discussed in subsequent paragraphs. Achieving this principle involves structuring the microservice architecture with the use of interfaces and classes which allows for the reuse and light coupling of services.

Interface Segregation Principle (ISP)

This principle builds on the Liskov substitution principle and it simply advocates for ensuring that interfaces used for each service are specific for the users who interact with them solely. This ensures that the interface delivers the specific function intended by the service created. This would in turn minimize service interdependency among various services and ensure service application autonomy, enabling it to achieve the desired scalability and overall efficiency possible.

This, alongside the Liskov substitution principle, allows for seamless microservice application evolution over a given cycle. To achieve this, it is important to ensure a minimal reliance of the service on external dependencies and also declare explicit and distinct functions for each service.

Dependency Inversion Principle

This principle negates the age-long tradition in which high-level modules and services tend to depend on smaller low-level services to achieve the necessary efficiency and correctly perform their designated function. It now implies that the high-level services/modules should not depend on anything from the low-level services and both should only interact based on the existing abstraction. In our case, this implies that the interfaces already discussed earlier.

This principle, in line with the other principles, permits easy scaling of each service or module in question and also allows for service reuse or substitution whenever such is needed. This principle has also revolutionized the way applications get built as they now delineate the functions and autonomy of each service in the application.

Additional Information

So far, we have shed light on the SOLID microservices design principles. However, other additional tips which could be of great help when building microservices include:

Availability Over Consistency Principle

This principle is based on the CAP theorem (consistency, availability and partition tolerance. Hypothetically, a system should have all these components implemented and fully functional but in reality, this isn’t so. Ensuring these works often results in network lags, which affects system efficiency, resulting in the need for tradeoffs among these components.

In the case of microservices development, the need for a service to be continually consistent in providing an updated response to a request gets overridden by the need for the service to be available with minimal downtime. Eventually, the overall microservice consistency is achieved during a given period via conflict resolution techniques and other consensus protocols.

Easy Deployability Principle

Unlike conventional monolithic applications, deploying microservices is a bit complex as it requires ensuring seamless communication across various deployments. However, this can be achieved by mastery of some techniques.

Firstly, it's important to possess knowledge of containerization and containerization tools such as Docker. Additionally, knowledge of orchestration tools like Kubernetes is an additional advantage. Adequate knowledge of Infrastructure as Code tools such as Terraform also helps as it gives the developers great control over the application and allows for easy versioning. Provision of monitoring and observability tools to help detect any anomaly in the operations.

Conclusion

With this, we have come to the end of the tutorial. We hope you’ve learned essentially about the principles and other best practices to have in mind when building microservices and other distributed applications.

Feel free to drop comments and questions in the box below, and also check out my other articles here. Till next time, keep on coding!

How to Build Resilient Microservice Systems – SOLID Principles for Microservices