Microservices are an accelerating trend thanks to rousing endorsements from the likes of Google, Netflix, and Amazon. The microservice architecture is advantageous for it’s scalability, agility and flexibility.
In contrast, the monolithic approach is the traditional tried-and-true model for building software. It’s much easier to debug and test. But how do you know which approach is best for your organization?
In this article, we look at the key differences between using a monolithic and microservices architecture as well as their inherent strengths and weaknesses.
What is a Monolithic Architecture?
The monolithic architecture is considered to be the traditional way of building an application.
A monolithic application is usually built as a single unit and indivisible unit, generally comprising of the following layers:
- A database, usually an RDBMS (relational database management system), that consists of many tables.
- A server-side application that handles and serves client-side requests, retrieves and stores data from/to the database and executes business logic.
- A client-side UI (User Interface) that generally consists of HTML and/or Javascript pages running on a browser.
The above layers group together to form a single logical executable. A monolithic application usually has one large codebase and lacks modularity.
If any updates are needed in the system, developers must build and deploy the entire stack at once.
What is a Microservices Architecture?
The microservices architecture breaks down an application into a collection of smaller independent units.
These units carry out application processes as separate services, each of which perform specific functions and have their own business logic and database.
The microservices architecture is an approach to developing a single application as a suite of small services.
The entire functionality is split up into independent modules that communicate with each other through defined APIs.
Each service has its own scope and can be deployed, updated and scaled independently. There is little to no centralized management of these services.
In contrast to a monolithic architecture, the functionality of microservices are expressed formally with business oriented APIs.
They encapsulate a core business requirement and the implementation of the service is hidden as the interface is defined in business terms.
These services are adaptable for use in multiple contexts and can be reused in multiple business processes or over different channels.
Due to the application of the principle of loose coupling, dependencies between services and their consumers are minimized.
This allows service owners to roll out any updates to the implementation of the services without any impact to the users.
Strengths and Weaknesses of Monolithic vs Microservices Architecture
Although the monolithic architecture seems to be quickly surpassed by microservices, it still has some advantages.
Software development processes differ quite a bit between the two architectures. The strengths and weaknesses of each are detailed below:
Monolithic Architecture Advantages
1. Simple to Develop
Since application development processes are standardized, they can be taken over by an engineering team with the right knowledge and skills.
2. Simple to Deploy
With monolithic applications, several deployments don't need to be handled versus using a microservices architecture - usually just one file (e.g. JAR/WAR) can be deployed.
3. Easier to Debug and Test
Since a monolithic application is a single unit, it is easier to debug code and end-to-end tests can be done much more efficiently.
4. Less Cross-Cutting
Monolithic applications have fewer cross-cutting concerns such as logging, caching, audit trails and performance monitoring. Since these processes are running through the same application, it is easier to handle them.
5. Performance
There can be performance advantages with monolithic applications since all communication is local, which is faster than inter-process communication.
Monolithic Architecture Disadvantages
1. Understanding
When a monolithic application scales, it generally becomes too complicated to be understood. Such a complex codebase within one application usually becomes hard to manage.
2. Making Updates
It is harder to implement changes in such large and complex applications with high tight coupling and entanglement. Any updates to code affect the entire system so they have to be coordinated. This makes the processes longer and increases overall development time.
3. Technology Barriers
Monolithic application components cannot be scaled independently - only the entire application at once. It is therefore quite problematic to apply a new technology without rewriting the entire application.
4. Scalability
Individual components cannot be scaled independently (only the whole application) whereas microservices can. Therefore, if a single component is facing large traffic volumes, the whole application needs to be deployed across multiple servers. This is very inefficient and consumes unnecessary resources.
Microservices Architecture Advantages
1. Decoupled Components
Since all services in a microservices application can be built, deployed and updated independently, they have more flexibility versus using a monolithic architecture. Any issue in one microservice does not have an impact on the entire application and only affects that service itself. It is also much easier to add new features to a microservices application.
2. Understanding
Since microservices applications are split up into smaller components and are better organized, they are easier to understand and manage. Developers can focus on specific services related to the business requirement they are trying to realize.
3. Scalability
Each component in a microservices application can be scaled independently, making the entire process more cost and time effective.
4. New Technologies
Each microservice can be built using various tools and technologies that are better "fit for purpose". Furthermore, new technologies can be added more easily to each microservice as needed without affecting the entire application.
5. Higher Agility
Any updates required to a specific microservice can be rolled out more easily and without any effects on the whole application.
6. Performance
Microservices applications can also have better performance depending on the architecture, since the core services can be isolated and scaled independently of the rest of the application.
7. Reuse
Unlike monolith applications, microservices can be consumed and reused by other applications and services through their APIs without direct coupling.
Microservices Architecture Disadvantages
1. Complexity
Since a microservices application is distributed, the connections between the various modules and databases have to be chosen. Also, since most services are independent of each other, they have to be deployed separately.
2. Cross-cutting
There are various cross-cutting concerns associated with a microservices application e.g. logging, metrics and health checks.
3. Debugging
Since the control in a microservices application flows over many services, it is harder to isolate and fix any issues that occur in the application.
4. Testing
Since there are a number of independent services in a microservices application, testing the application is more complex compared to monolithic applications.
5. Overhead
Microservices applications are usually deployed on their own virtual machines or containers, which adds operational overhead.
6. Network Latency
Microservices architecture usually have higher network usage since they interact with each other using remote calls, which can cause network latency.
