In the field of software development, it is very popular to create applications with independent services. This architecture or style is known as microservices. Spring Boot is a popular Java framework that provides us with an excellent platform for developing microservices due to its simplicity and extensive ecosystem. In this article, we will explore the complete architecture of Spring Boot microservices in details step by step.

The Architecture of a Spring Boot Microservices System

To understand the complete architecture of Spring boot microservices, imagine we are using an e-commerce application. We open the app, browse products, place an order, make payment, and receive a notification. This entire journey goes through multiple layers of the microservices architecture in a perfectly organized sequence.

Step 1 — Request from Client

The user interacts with a client application such as a mobile app or a web app. The client never contacts any microservice directly. Instead, it sends every request to a single entry point in the backend called the API Gateway.

Step 2 — API Gateway Takes Control

The API Gateway receives the request and decides which microservice should handle it For example:

• If the request is login or signup → It forwards to the Authentication microservice
• If the request is to browse products → It forwards to the Product microservice
• If the request is to place an order → It forwards to the Order microservice

If the request is to place an order → It forwards to the Order microservice

• Validate authentication token
• Apply rate-limit rules
• Log request details

From the client’s perspective, the whole backend feels like one application, even though it is actually made of many microservices.

Step 3 — Microservices Handle Business Logic (Example Spring Boot Microservice)

Once the request reaches the correct microservice, that service performs its own job. Each microservice has its own:

• Controller (REST)
• Service layer (business logic)
• Repository/DAO (database operations)

If the microservice needs extra information from another microservice, it sends an internal REST API call for Example

• Order Service calls Product Service to get price
• Payment Service calls Order Service to validate the amount
• Mobile team consumes APIs

This cooperation happens automatically behind the scenes.

Step 4 — Service Registry Enables Discovery

Every microservice that starts registers itself with the Service Registry. So when one microservice needs to call another, it doesn’t use a hardcoded URL. It simply asks the registry:

“Where is the Product Service right now?”

The registry replies with the current location so services can communicate smoothly even if they scale or move.

Step 5 — Config Server Supplies Configuration

Shared configurations — like database URLs, logging settings, limits, and feature flags — are stored in a Config Server. Microservices fetch config from there so settings are consistent and dynamic across the whole system.

Step 6 — Load Balancer Handles High Traffic

If one microservice has several instances running to handle high load (for example, 10 copies of Payment Service), the Load Balancer distributes the traffic intelligently across them. This ensures:

• Faster performance under high load
• No single instance becomes overloaded

Step 7 — Circuit Breaker Adds Fault-Tolerance

If a microservice being called is temporarily down or slow, the Circuit Breaker protects the system. Instead of repeatedly calling a failing service and crashing everything, it stops the calls and provides a fallback response. This keeps the whole application stable even when one microservice is unhealthy.

Step 8 — Messaging for Event-Driven Flow

Certain actions need to trigger further actions automatically without holding up the user request. For that, services use a message broker like Kafka or RabbitMQ. For example:

• After successful payment → Payment Service publishes an event
• Notification Service receives the event and sends email/SMS
• This makes services independent and fast.

Step 9 — Logging, Tracing & Monitoring Help in Operations

Since dozens of microservices run separately, logs and traces must be collected in one place. Centralized logging, distributed tracing, and monitoring dashboards allow engineers to observe the whole system as if it were one application.

Step 10 — Database Layer

Each microservice uses its own database, based on what fits its responsibility. Databases are not shared, which prevents coupling and improves performance.

Step 11 — Cloud, Docker & Kubernetes Handle Deployment

Finally, all microservices run as Docker containers and are deployed on a cloud platform.

Kubernetes manages:

• Auto-deployment
• Auto-restart when a service fails
• Auto-scaling during traffic spikes
• Zero-downtime upgrades

This makes the entire architecture strong enough to support millions of users.

Final One-Line Essence of Architecture

The architecture takes a user request from the client, passes it through the API Gateway, processes it inside microservices supported by discovery, config, load balancing, resilience, messaging, logging, tracing, and monitoring, stores or retrieves data from independent databases, and finally runs everything at scale through Docker, Kubernetes, CI/CD, and cloud.

1️⃣ What exactly is Microservices Architecture?

Microservices architecture means building one large application as multiple small applications, where each small application (microservice) handles only one business responsibility.

• Works independently
• Has its own codebase
• Has its own build and deployment
• Has its own database
• Exposes REST APIs so other services can communicate

All the microservices together form the final system. This makes the application easier to develop, deploy, scale, and maintain compared to a monolithic application.

2️⃣ Role of Client Applications in Microservices

Microservices do not directly interact with end-users. Users access the system through different client applications like:

• Mobile Apps (Android / iOS)
• Web Applications (Angular / React / Vue / Spring MVC)
• Desktop Apps
• IoT devices
• Third-party systems such as Salesforce / Partner Applications

All these client applications need data and services from the backend. Therefore, the backend must expose services in a secure and consistent manner — which is handled through the API Gateway.

3️⃣ API Gateway Why This Component Is important

In a real microservices system, there may be 10, 20, or even 50 microservices running. If client applications directly speak to each service:

• Clients would need to know every service URL.
• Clients would need to manage security and valid tokens
• Versioning and routing become impossible to maintain
• Any internal microservice change could break external clients

To avoid this complexity, all requests from all clients first go to the API Gateway. following are the Purpose of API Gateway

• Provide one single entry point for client applications
• Route each request to the correct microservice internally
• Validate authentication tokens (e.g., JWT )
• Apply rate-limiting if too many requests arrive
• Perform request logging and filtering

Because of the API Gateway, client applications remain simple and insensitive to internal microservice changes

4️⃣ How Microservices Communicate with each other?

Sometimes one microservice needs data from another service. for Example we have three microservices in spring boot application:

• Order Service needs data from Product Service (to check price)
• Payment Service needs data from Order Service (to verify amount)
• Notification Service needs data from Payment Service (to send OTP or purchase receipt)

In a monolithic application, modules call each other directly in memory. In microservices, direct method calls are not possible because services are deployed separately. So microservices communicate using REST APIs. following is the internal flow :

• One microservice plays the role of API Provider
• Another plays the role of API Consumer
• This keeps the whole architecture loosely coupled

5️⃣ Why Microservices Use Multiple Databases (Not One Shared Database)

In monolithic architecture, all modules share one large database. This has many problems:

• High dependency — changes in one module affect others
• Very large schemas that are hard to maintain
• Locking and performance issues

Microservices architecture avoids this by using database-per-service. Each microservice manages its own data fully. It has full control over schema, table structure, and storage engine. This freedom helps performance and reduces dependency between teams. Also, every microservice can use the most suitable database type:

6️⃣ Distributed Operation Challenges — and How Microservices Solve Them

When an application runs as many microservices rather than one, certain challenges appear:

To handle all these challenges, microservices architecture includes special support tools and patterns, not only REST APIs.

7️⃣ Complete Set of Required Components in a Microservices Architecture

Below is a complete list of required components (with explanation) — rewritten cleanly and clearly:

API Gateway

Handles all incoming requests from clients and forwards them to correct microservices. Also applies authentication, routing, Rate Limiting, and request logging.

Service Registry & Discovery

A dynamic registry that stores the current locations of running microservices. Services register themselves when started and discover other services when needed.

Config Server

Stores all common configuration in one place rather than repeating it in each microservice. Makes updates safer and much easier.

Load Balancer

Distributes traffic across different instances (copies) of the same microservice. Ensures equal distribution and prevents overload.

Circuit Breaker / Resilience

Protects the system when a service is failing. Stops repeated calls to a failing service and returns fallback responses to prevent system collapse.

Message Broker / Event Bus

Allows microservices to communicate asynchronously using events (e.g., “Order Placed → trigger Payment → trigger Notification”).

Centralized Logging

Collects logs from all microservices into one searchable dashboard. Makes debugging and root cause analysis much easier.

Distributed Tracing

Tracks the journey of one request through multiple services and measures time spent at each step.

Monitoring & Metrics

Displays dashboards with service health, resource usage, error rate, and performance so teams can take quick action.

Security Layer

Provides authentication and authorization for APIs. Implemented using OAuth2, JWT, Keycloak, or Spring Security.

8️⃣ What This Entire Setup Achieves

With all the above pieces working together, microservices architecture gives:

• Independent development – Each team focuses only on its own service.
• Independent deployment – Only the updated service gets deployed — not the whole system.
• Zero-downtime releases – Thanks to CI/CD pipelines, containerization, and rolling updates.
• Technology freedom – Each service can choose Java, Node.js, Python — whatever fits its features
• Better reliability – Even if one microservice goes down, others continue working.

This is why Microservices + Spring Boot + Cloud + DevOps has become the standard pattern for large, fast-changing enterprise applications

Conclusion

Microservices are not just multiple APIs, but many small spring boot applications that together form one big system. Each spring boot service handles one business task and runs independently, but they cooperate using API Gateway, Service Registry, Config Server, Load Balancer, messaging, logging, tracing, monitoring, Docker, Kubernetes, and CI/CD pipelines. When all of these pieces work together, the system becomes scalable, reliable, easy to update, and ready for cloud deployment.