Microservices Communication: REST vs Messaging vs Event Streaming
Pragya Mutluru
Microservices are like people — they need to talk to each other to get work done. Just as people can communicate via text, phone calls, or even group chats, microservices also have various ways to exchange information.
The three most common communication styles in microservice architectures are:
REST (Synchronous)
Messaging (Asynchronous via Message Broker)
Event Streaming (Asynchronous via Event Bus like Kafka)
Each approach has its strengths and trade-offs. Let’s explore when to use what, and how to avoid common pitfalls.
REST: Simple, Familiar, and Synchronous
REST (Representational State Transfer) is the most well-known and widely used form of communication between services. It uses standard HTTP verbs (GET, POST, etc.) and relies on synchronous request-response semantics.
When to Use REST
When real-time response is needed.
When service-to-service calls are minimal.
When interaction is transactional (e.g., login, data fetch).
When your system needs human-readable APIs for external integrations.
Trade-Offs
Tight coupling: If Service A depends on Service B’s availability, a failure can cascade.
Scalability bottlenecks: RESTful APIs don’t handle spikes as gracefully.
Latency-sensitive: Can slow down chains of services due to synchronous waits.
Example: A user registration service calls a profile service over REST to immediately create a default profile.
Messaging: Decoupled and Resilient
Message-based communication involves a message broker (like RabbitMQ or ActiveMQ) that receives and routes messages to consumers. This enables asynchronous communication.
When to Use Messaging
When decoupling services is a priority.
When operations don’t require an immediate response.
For retryable, background jobs (e.g., sending emails, notifications).
When you want reliable delivery (with retries, dead-letter queues).
Trade-Offs
Complexity: Requires message formats, consumer groups, error handling.
Observability challenges: Harder to trace message flow end-to-end.
Eventually consistent: You can’t guarantee immediate data availability.
Example: An order service sends a message to the shipping service once an order is placed. The shipping happens later, but the order flow continues.
Event Streaming: Real-Time & Reactive
Event streaming (e.g., with Apache Kafka or AWS Kinesis) enables services to publish and subscribe to immutable event logs. Events are stored and replayable.
When to Use Event Streaming
For real-time analytics and reactive systems.
When building event-driven microservices.
For decoupling producers and multiple consumers.
When you need to persist a history of events.
Trade-Offs
Steep learning curve: Requires understanding partitions, offsets, replay semantics.
Eventual consistency: Like messaging, you give up strong consistency.
No guaranteed ordering across partitions.
Example: A payment service publishes a
PaymentCompletedevent. The billing, inventory, and notification services all consume it independently.
How to Choose the Right Communication Style
| Criteria | REST | Messaging | Event Streaming |
| Synchronous | ✅ | ❌ | ❌ |
| Loose Coupling | ❌ | ✅ | ✅ |
| Ordering Guarantees | ✅ | ✅ (within queue) | Partial (partition) |
| Retry Mechanisms | ❌ | ✅ | ✅ |
| Multiple Consumers | ❌ | ✅ | ✅ |
| Historical Replay | ❌ | ❌ | ✅ |
| Real-time Analytics | ❌ | ❌ | ✅ |
Real-World Tip: Mix & Match!
You don’t need to pick just one. Most modern systems combine all three:
REST for user-facing APIs or command-style requests.
Messaging for decoupled workflows like order processing or email queues.
Event streaming for audit logs, analytics, and complex pipelines.
A smart architecture chooses the right tool for the right job, balancing performance, maintainability, and complexity.
TL;DR
Use REST when you need immediate responses and simplicity.
Use Messaging when you want decoupled services and guaranteed delivery.
Use Event Streaming when you need real-time insights or many consumers reacting to the same event.
Modern microservices aren't about dogmatic tech choices — they're about designing systems that are responsive, resilient, and ready for change.
What Do You Use?
Are you using REST, messaging, or events in your microservices? What patterns have worked well for your team — and what didn't?
Drop a comment or connect — I’d love to hear about your experience.
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