Microservices are an architectural style in which an application is built as a set of small, independent services, each responsible for one specific business capability. Each service is developed, deployed and scaled separately, and communicates with the others through well-defined interfaces.
The underlying idea is simple: instead of one giant application where everything is intertwined, you build autonomous pieces that can be changed, tested and scaled without touching the rest.
What problem do microservices solve?
As an application grows, the code tends to become an ever larger, more tangled block. A small change forces you to test and deploy the whole system. A demand spike in a single function forces you to scale the entire application. And when several teams work on the same block, they end up stepping on each other.
Microservices break that block into parts with clear responsibilities. Each team owns its service, deploys it at its own pace and scales it according to its own demand. The result is faster delivery and a system that tolerates failure better.
Microservices versus a monolith
It is not that one model is good and the other bad: they fit different stages of a product.
| Monolith | Microservices | |
|---|---|---|
| Structure | A single piece | Independent services |
| Deployment | All at once | Each service separately |
| Scaling | Everything scales | Only what is needed scales |
| Teams | High coordination | Autonomous teams in parallel |
| Failure impact | Can affect everything | Contained to the service |
| Starting point | Simpler at first | More complex to operate |
Put simply: a well-structured monolith is easier to start and is often enough for small products; microservices shine when the application grows, when several teams move in parallel and when different parts need to scale differently.
How do microservices work?
Each microservice exposes its functionality through an API and keeps its own data. To talk to each other, services use direct calls (for example, HTTP requests) or asynchronous messaging through queues and events, which decouple processes so each part can move at its own pace.
A few common pieces appear around that idea:
- API gateway: receives external requests and routes them to the right service.
- Asynchronous communication: queues and events so one service does not sit waiting on another.
- Data per service: each service manages its own database, which reinforces its independence.
- Observability: traces, metrics and logs to understand a system spread across many pieces.
How microservices are built on AWS
AWS provides the building blocks to run microservices without managing the underlying platform:
- Containers with Amazon EKS (Kubernetes) or Amazon ECS: package each service and orchestrate it at scale.
- Functions with AWS Lambda: run microservices by event, without managing servers.
- Amazon API Gateway: exposes and routes APIs securely toward each service.
- Managed messaging and queues: decouple services so they scale independently.
Each microservice can live in a container or in a serverless function, depending on its load, and scale on its own without affecting the rest.
Business benefits of microservices
- Faster delivery: teams deploy their service without waiting on the rest.
- Granular scaling: only the part that receives demand scales, not the whole application.
- Contained failures: a problem in one service does not bring down the entire system.
- Evolution in parts: you can modernize or rewrite one service without redoing everything.
When it makes sense (and when it does not)
Microservices are not a mandatory destination. They add the most value when the application has already grown, when several teams share the system, or when different parts need to scale differently. For a small product or a small team, starting with a well-structured monolith is usually simpler, cheaper to operate and faster to evolve.
A frequent and sensible path is to start with a tidy monolith and, when growth justifies it, split into microservices the parts that need it most. The right decision depends on the size of the product, the teams and the demand pattern.
Microservices as part of modernization
Adopting microservices is usually part of a broader modernization journey, not a one-day leap. It helps to lean on containers and Kubernetes, on Docker to package each service and, where it makes sense, on serverless to run by event.
At Caleidos we support that transition within our application modernization and cloud native development practices, with production cases documented in our case studies.
Frequently asked questions
What are microservices in simple terms? An architectural style where the application is built as small, independent services, each in charge of one business capability and deployed separately.
How do they differ from a monolith? A monolith is a single piece deployed and scaled as a whole; microservices deploy and scale separately, and a failure stays contained to its service.
How are they built on AWS? With containers on Amazon ECS or Amazon EKS, event-driven functions with AWS Lambda, and Amazon API Gateway to expose APIs.
Are you evaluating a move to a microservices architecture?
Let’s talk about your case and we will give you a concrete recommendation on when and how to adopt microservices on AWS.
