Monolithic vs. Microservices - Which One Is better?

Technology has made exponential advancements during the past decades, leading to the creation of new concepts in software development. The modern demands of the market, the client’s requirements, and other factors required a thorough re-engineering of the traditional methods of monolithic application architecture design. Enter microservices.

This writeup intends to describe the specifics and weigh the benefits of microservices vs monolith approach to deploying applications. For those who have already made the decision to switch, we explain how to make the transition from a monolithic architecture to microservices with the help of AWS.

Key Points to Discover

This post will enable its readers to:

• Develop a good understanding of what monolithic architecture is and dive deep into the concept of microservices, as well as discover the key differences in these two approaches.
• Understand the necessary steps for gradually breaking down large monolithic applications into independent services.
• Identify the principles of maintaining a good microservice application architecture.
• Utilize multiple AWS technologies to make a seamless transition to microservices.

Microservices vs Monolith Architecture: An Overview

Application architecture is something every developer is concerned about, regardless of which phase they are at with a product. Previous generations had most software companies, large businesses included, relying on pure monolithic applications. What this essentially means is that the whole application runs as a single service, and more or less each container in the application has access to the same set of features.

The reason why this is not a favorable approach in the modern world is that having an application architecture like this makes it difficult to scale. If one particular feature crashes, all other features will experience the same downtime, inevitably leading to extremely unsatisfied customers.

Another downside of monolithic application architecture is that when the demand for a particular feature increases, the developers are forced to increase the resource limits not just for that one feature but the entire application as a whole. This is because each feature is not isolated from the others. This generates unnecessary costs, especially when the application is large and complex.

This is where the microservice architecture comes in as a solution. Each feature of the application runs on its container and is isolated in a way that it can be scaled or updated without having to cause any impact on other application features.

You could imagine that microservice architecture resembles a circuit operating in a parallel series configuration. Thus in microservices, if a single feature were to break down, the others would not be affected.

There are essentially two ways you can implement a microservice architecture:

• Synchronous. This implementation relies on direct HTTP requests from one feature to another. This usually leads to creating dependencies among features as it makes it mandatory to interact with, for example, a database of another feature. This is considered an anti-pattern.
• Asynchronous. This method is based on an event bus and having a database for each separate feature even if the data relevant to that feature is already in another database. This ensures maximum isolation but leads to data duplication, which is a concern that drives away quite a few developers, however, the cost that comes with it is relatively little to none compared to the benefits.

Principles of the Microservice Architecture

Microservices provide solutions to many real-world problems, but if stringent guidelines and limitations are not followed during the development phase, it can lead to a  hybrid application architecture that may limit the potential of your application. These principles should be followed  to ensure a healthy microservice architecture:

• Each feature of the application must be isolated and not interact with the database of another feature. In other words, there should be no dependencies.
• Avoid coupling your microservices too tightly to circumvent the issues with scaling and maintainability.
• Consider decentralization over centralization to ensure maximum isolation and to allow independent deployments.

Disintegrating the Monolith Into Microservices Using AWS

Now that you understand the underlying caveats of the monolithic application architecture and the reasons why you should make the transition to microservices, you would want to start disintegrating your monolithic applications. This can be done in these three steps:

1. Containerizing the Monolithic Application

Container technology has been widely acclaimed in contemporary application development. Containers essentially allow easy packaging of the dependencies, code, and configuration of your application into small blocks to ensure consistency across environments. You can make use of the Amazon Elastic Container Registry (ECR) and Docker to achieve containerization.

Docker is a PaaS that achieves containerization through virtualization at the operating system level to ensure maximum environmental consistency, while Amazon ECR is a docker container registry meant to store different containers as a repository which helps keep management and deployment of Docker containers relatively easy.

2. Deployment of the Containerized Monolith

After containerizing the monolith, comes its deployment. Amazon Elastic Container Service can be used to draw up a cluster of different Amazon EC2 instances that allows clients to interact with your application through a set of target groups and a load balancer.

3. Disintegration of the Monolith

The second step is to identify the different features of your application and how to efficiently isolate them. It must be ensured that no feature interacts with the database of another feature which can indirectly create a dependency.

Once each feature is separately identified, you can assign a unique target group to each of them and have all the traffic load balanced before it reaches each feature. To do this, you need to ensure that each container is separate, which means that there should be repositories storing the containers of each feature. Amazon ECR can be used to create repositories that hold the containers of each service.

Deploying the Microservices

After the monolithic application has been containerized and broken down to its simplest units, you can smoothly transition to the microservice architecture. It is very important to avoid having any downtime because this transition can take from days to weeks depending on how many features there are and how complex each feature is.

Following the aforementioned procedure, traffic can be gradually diverted to the feature containers with the help of Amazon Load Balancer. Once it is done, each target group can be configured and you can gradually transition from the monolith to the microservice architecture.

Summary

That was a tough read, but worth the effort because now you understand the reasons behind the modern trend of microservices, and that:

• Monolithic architecture exists when all the resources, business logic, and complexities for all the features reside in one single application.
• Microservice architecture is in place when the resources and the business logic for each feature are isolated and work as independent applications.
• Decentralization should be preferred during disintegration to ensure independent applications.
• AWS technologies like Amazon ECR, EC2, and LB can assist in a smooth transition from a monolithic architecture to microservices with minimal to no downtime.

Resources

Feel like reading more? Check these links out:

• Docker Documentation contains a wealthy amount of knowledge on how containers work at a very low level.
• Amazon Web Services Documentation is a hub for references and documentation of multiple technologies provided by Amazon.
• Microservices.io is a hub for all things microservices, if you wish to get an in-depth understanding.