What is microservices architecture?

Microservices architecture is a method of developing software systems that structures an application as a collection of loosely coupled services, each focusing on a single function or business capability. Each service operates within a discrete, confined context, communicating with other services through well-defined interfaces — typically APIs. This approach provides a more flexible and scalable alternative to the traditional monolithic architecture and has gained widespread adoption among organizations building large-scale systems.

This article provides an overview of microservices architecture, highlighting how it differs from monolithic applications. We explore its core principles, benefits, challenges, design strategies, testing methods, and the technologies that support it.

Microservices architecture vs monolithic applications

Microservices gained traction in the early 2010s as companies like Netflix and Amazon demonstrated its effectiveness in handling large-scale, complex systems. This approach rapidly gained popularity as it aligned well with the increasing adoption of cloud computing and agile methodologies, offering a solution to the scalability and flexibility limitations of traditional monolithic architectures.

Let’s review a few of the key differences between monolithic and microservices architectures, including their structure, deployment requirements, and scalability.

Factors	Monolithic applications	Microservices
Structure	Unified, indivisible, interdependent	Distributed, self-contained, autonomous
Deployment	All-or-nothing, rigid, high-impact	Flexible, easily updated
Scalability	More costly, less efficient	Cost-effective, on demand, automatable

Structure

A monolithic application is a single, indivisible unit with fully interconnected and interdependent components: The user interface (UI), business logic, and database access are all interwoven.

In contrast, a microservices application contains numerous independent services, each responsible for a specific functionality. To maintain autonomy, each service is self-contained with its own business logic and database.

This structural difference has a significant impact on the development and maintenance requirements for each architecture.

Deployment

Deploying a monolithic application occurs as a unified process. Even for minor changes, you must redeploy the entire application to update it, making this process bulky and inflexible.

The microservices deployment process is infinitely more flexible. Because each service contains all the code, logic, and operating information necessary to function, you can deploy any component independently. It means that rolling out updates or changes does not affect the entire application.

Moreover, this deployment flexibility — stemming from its underlying structure — substantially enhances your scalability options.

Scalability

Scaling traditional monolithic applications has always been challenging, often involving expanding the whole application to enhance the availability of one or two components. This process tends to be inefficient and cost-ineffective.

For example, imagine a web-based retail application. Under the monolithic approach, every aspect of the application — UI, payment processing, content management system, and order management — is part of a single, indivisible unit. Scaling up the application to handle an expected increase in traffic requires infrastructure upgrades for the entire application, even though only certain parts of the app, like the payment gateway and order management functionalities, anticipate increased demand.

This scenario can create massive resource use inefficiencies. Furthermore, this scaling is primarily vertical — adding more power to the existing server — restricting the monolithic application’s ability to adapt to variable demand levels once the traffic spike subsides.

In contrast, the autonomous nature of microservices means you can scale each service individually, optimizing resource allocation in response to dynamic workloads. To manage the increased load, you can simply add more instances of the payment gateway and order management across different servers. This horizontal approach is significantly faster and more cost-effective to implement than the monolith’s vertical approach. Moreover, options like automation allow you to adapt to changing traffic patterns near-instantaneously.

Core principles of microservices

Microservices architecture rests on three fundamental principles: modularity, independence, and the decentralization of data, all contributing to rapid development and deployment cycles.

Modularity

Modularity ensures that each service is self-contained and performs a specific function. Smaller, well-defined modules are easier to understand, develop, and maintain. If you are a developer working on our example retail application’s CMS, you do not need a comprehensive understanding of its user authentication and payment gateway.

You can even use different frameworks for different CMS components, like Vue.js for content rendering and Python for data management. Modularity enables this flexibility, as long as each service adheres to defined communication protocols.

Independence

The ability to develop and deploy services independently means you can change or update one service without affecting others or redeploying the entire application. If a security vulnerability arises in your application’s payment portal, you can release a patch rapidly or update to the newest framework version without interrupting the app’s other services.

This isolation also improves the application’s resilience and availability. Different teams can manage different services, allowing for parallel development and reducing coordination overhead.

Decentralized data management

Each service in a microservices architecture manages its own data, promoting autonomy and reducing external data dependencies. This principle also ensures greater consistency and data integrity within its scope.

Because a microservice controls its own data schema and storage mechanisms, you can choose the data storage technology that best suits it, whether a relational database, NoSQL database, or in-memory storage.

Decentralization also prevents the tight coupling that a shared data schema creates among its services. This separation reduces the risk of changes in one data model affecting others. For WingFits, this principle isolates proprietary business data from sensitive customer information and maintains the security of both.

Benefits and challenges of microservices architecture

As discussed, the microservices architecture offers some compelling benefits for teams building complex applications, including improved scalability, flexibility, and easier maintenance. It also helps expedite debugging through enhanced fault isolation and is better aligned with modern development practices like continuous integration and continuous delivery (CI/CD) and Agile methodologies.

However, microservices are not a perfect fit for every team or application type, so it is important to understand the challenges that may accompany it, particularly the increased complexity and monitoring requirements:

• Increased complexity — Managing the interactions between numerous distributed services is complicated and creates the potential for communication hiccups and network latency between service locations. Additionally, the need to handle each microservice independently underscores the importance of implementing robust testing and deployment pipelines, which can add to the technical complexity for less experienced teams.

• Management requirements — The distributed nature of microservices necessitates thorough monitoring, logging, and communication mechanisms. Given their inherent autonomy, monitoring these services requires various well-orchestrated communication methods.

Microservices architecture may not be suitable for every team or application type, particularly for small projects or teams with limited resources, as the complexity and overhead of managing multiple services can outweigh the benefits. It’s more suited for large-scale, complex applications requiring high scalability and flexibility. Basic criteria for determining whether microservices are right for you include the size and scope of your project, your team’s expertise in distributed systems, and the need for rapid scaling and development agility.

Designing effective microservices applications

Designing effective microservices applications involves adhering to certain guidelines and best practices:

• Domain-driven design (DDD) — Model each service around the business domain, ensuring it correctly aligns with a specific business function.

• Well-defined APIs — Tight coupling between services can lead to interdependencies that negate the benefits of microservices. Clearly defined APIs ensure loose coupling and service autonomy.

• Health monitoring — Implement automated service health checks and monitoring to detect and address issues early.

• Build for failure — Assume your services will fail, and design them accordingly. Include strategies for graceful degradation and quick recovery.

Testing strategies for microservices architecture

The distributed nature of the microservices architecture presents some unique challenges for application testing. Effective integration and end-to-end testing are crucial for ensuring service reliability and performance, as issues in one service can reverberate across others.

Integration testing

Integration testing determines whether independently developed software units work correctly once connected to other microservices. This often includes testing API contracts, data flow, and error handling between services. Strategies like consumer-driven contract testing, where consumers of a service define the expectations in a contract, help maintain compatibility between services.

End-to-end testing

End-to-end testing validates the entire software application from start to finish. It examines whether an application flow behaves as expected from a user’s perspective, covering all the operations the software performs during real-world use. Typically, this strategy tests everything from the UI to the back-end processes and databases.

End-to-end testing in a microservices architecture often requires setting up a testing environment that closely mimics the production environment, including all the interconnected services and their dependencies. Automated tests simulate real user scenarios to validate the integrated system, including user interface, APIs, and data processing. Due to the complexity and distributed nature of microservices, tools and frameworks that support service orchestration and mock external services are commonly employed to facilitate comprehensive and efficient testing.

Tools and technologies used in microservices delivery

Deploying, managing, and scaling microservices requires specialized tools and technologies, each contributing significantly to the architecture’s effectiveness and reliability.

Containers

Containers like Docker are lightweight virtualizations, encapsulating a microservice and its dependencies to keep them isolated and portable. This isolation ensures that the microservice runs consistently across different environments, from development to production. Their lightweight nature enables efficient use of system resources and faster startup times — critical for scaling.

Container orchestration

Container orchestration tools like Kubernetes automate deploying, scaling, and managing containerized applications. Kubernetes can automatically scale containers based on demand, efficiently distributing network traffic among containers and services. This approach ensures optimal resource use and high availability.

APIs

APIs are essential for enabling secure, standardized communication among microservices. They facilitate the loose coupling that is vital for the efficiency and reusability of microservices applications. APIs also foster integration with external services and third-party applications, broadening each application’s potential functionality and reach.

Event streaming

Event streaming platforms like Apache Kafka enable microservices to communicate asynchronously via events. This capability aids in decoupling services in distributed systems and supports real-time data processing and analytics — essential for data-driven microservices.

Serverless computing

Serverless computing abstracts away infrastructure management, letting you focus on writing code and business logic rather than overseeing servers. Moreover, it offers an on-demand execution model where you pay only for what you consume, making it cost-effective, especially for microservices with variable workloads.

CI/CD

CI/CD tools like CircleCI automate the software delivery process, spanning from code integration to deployment. They automate the build, test, and deployment processes, enabling rapid iteration and frequent deployment. These CI/CD practices are essential in a microservices environment. They support rapid development, testing, and deployment cycles, ensuring that you can update services frequently and reliably while minimizing manual errors.

Conclusion

Microservices architecture represents a significant shift in how we develop, deploy, and maintain applications. Despite their increased complexity and management challenges, the benefits of microservices are clear. The emphasis on modularity, independence, and decentralized data management appeals to many organizations seeking agile and robust software solutions.

Understanding these dynamics is key to harnessing the full potential of microservices. If your team is interested in adopting microservices, a robust CI/CD pipeline is essential for effectively managing the complexity that comes with building, testing, and deploying microservices architecture. To build the foundation your team needs to adopt microservices with minimal friction and maximum efficiency, sign up for a free CircleCI account today and kickstart your journey towards successful microservices development.