With microservices projected to grow globally at a 22.5% rate between 2019 and 2025, the choice between monolithic and microservices architectures needs to be carefully considered. If you are wondering what microservices are best suited for, or whether your business should stick to monolithic or switch to microservices, here are a few cardinal points to take into consideration.

What Is Monolithic Architecture?

A monolithic application is built on a single code base with a variable number of modules. The number of modules depends on the complexity of the business and its technical features. The whole application—and dependencies, when applicable—are built on a single system with a single executable binary for deployment.

A monolithic architecture has distinct advantages and disadvantages that should be evaluated when deciding when selecting the optimal type of architecture for the application.

Monolithic architecture pros:

Fewer cross-cutting concerns: The majority of applications typically have a large number of cross-cutting concerns. Running them all on a monolithic architecture facilitates hooking up components.
Less operational overheads: Avoids the additional costs stemming from microservices such as interservice communication, service discovery and registration, load balancing, decentralized data management or distributed logging, for example.
Complex testing: Testing for microservices is considerably more complex than for monoliths.
Better performance: As shared-memory access is faster than interprocess communication, a monolithic architecture typically has better throughput performance.

Monolithic architecture cons:

Overly tight coupling: Entanglement increases the difficulty of isolating services for upgrades or independent scaling when the application evolves.
More difficult to understand: As the application grows and the number of layers and dependencies increases, understanding the system becomes increasingly difficult.
Slow build and test create releases: Upgrades imply recoding the entire application to factor in the dependencies and side effects.
Hard to distribute development: Tightly integrated applications are difficult to break into chunks, which complicates the creation of a distributed team effort.
Usually requires opting for a single programming language: Integrating more than one language in a monolithic application is fraught with challenges, typically preventing the integration of components written in a different language, which might limit the flexibility of adding features best suited to an external language.
Complicates the adoption of third-party tools: Adding self-contained third-party components, for example, cloud-native, to a single code base with multiple dependencies requires complicated hookups to different layers of the monolithic application.

What Is Microservices Architecture?

Microservices architecture is designed to accommodate the need for large application development by providing a suite of modular components and services.

When considering what microservices are particularly well-suited for, the following advantages and disadvantages should be taken into account:

Microservices pros:

Better organization: Microservices are organized around business and technological capabilities, in units that are independently deployable.
Decoupled: Each unit can be independently upgraded without requiring a complete overhaul of the application.
Performance: Flexibility in opting to privilege performance or flexibility as needed, including independently scaling heavily used services by isolating them from the remainder of the application.
Fewer mistakes: The hard-to-cross boundaries between microservice units limit the technical possibility of generating mistakes, notably cascading ones.
Easier onboarding of new developers: They only need to master the microservice unit they will work on instead of the entire application architecture.
Scalability: Each microservice can be scaled independently, while also adding new components.
Improved fault isolation: As modules work independently from each other, a failure in one module does not affect another.
Elimination of vendor or technology lock-in: As each microservice module can be operated independently, replacing underperforming modules with better ones from an alternate vendor is relatively easy.
Ease of understanding: As services are broken down into modules, understanding the functionality of a module is easy for developers.
Smaller and faster deployments: Each service can be scaled independently as needed, instead of scaling the entire application. This can lead to cost savings.

Microservices cons:

Cross-cutting concerns: Microservices require handling cross-cutting concerns such as externalized configuration, logging, health checks, metrics, service registration and discovery and circuit breakers, as well as those specific to the technologies used by the microservices.
Higher operational overhead: Microservices deployment typically leads to an increase in the number of units and containers, increasing the management and operation cost overheads.
Security threats: Microservices architecture presents an expanded attack surface. Securing a containerized application requires managing privileged access at image, container, node, pod and namespace levels, ensuring encrypted tunneling from ingress to egress and other elements that require baking in security from the beginning.
Multiple complexities requiring management:
- Communication between services on a technological level, and between teams on an operational level.
- Selecting the optimal pattern from the several microservices patterns available.
- Provisioning sufficient IPs.
- Provisioning resources (memory, CPU, disk) to accommodate each cluster requirements.
- Maintaining multiple programming languages and frameworks.
- Handling the incompatibilities between existing tools and new service dependencies.
- Accounting for automation tools for each service requiring individualized testing and monitoring.
- Achieving data consistency between each service’s individual database and transaction management system.
- Handling the number of processes that can grow exponentially when load balancing and messaging middleware are considered.
- Provisioning for the increase in documentation overhead stemming from the need to keep schemas and interface documents up to date.
- Refactoring of an application built on monolith architecture is a massive undertaking for large enterprise applications.
Complicated global testing: Global testing requires that each dependent service be tested first. This can be partly assuaged with automated testing.
Difficulty in debugging problems: Debugging requires inspecting each service log independently, increasing the workload.
Deployment challenges: Microservices are written in a variety of frameworks and languages and require distinct resources, scaling and monitoring, making orchestrating the deployment challenging.
Large versus small product companies: Though the benefits of microservices are invaluable for large companies, adopting a microservices architecture creates overwhelming complexities leading to slower implementation and unnecessary cost increases for small companies.
Higher costs: Without careful and strategic planning, cloud service bills may balloon due to the increase in data stemming from intraservices calls and the increase in resource requests to account for scalability and lack of friction.
Cultural changes: Microservices require the company to have an agile DevOps culture.

As microservices architecture provides a better way to manage growing data sets, leverage cloud storage and automation and deploy solutions fast, microservices are usually preferable to monoliths. However, they might not always be the best choice for an organization. Before opting for microservices, a careful examination of your company culture and business objective is imperative.