Why is REST not always the best choice for microservices?

REST is not always optimal for microservices because it was designed for client-server applications, not for internal communication among many services. At scale, it starts to limit flexibility and performance.

#1. High overhead

Every REST request is a separate HTTP connection with JSON serialization and headers. For internal calls between services, this creates unnecessary load and latency.

#2. Complexity in long call chains

REST requires sequential requests: one service waits for another's response. In a distributed system this slows down the data flow and increases the risk of failures.

#3. No native support for event-driven behavior

REST is a synchronous protocol. If you need to notify other services about events ("order created", "payment completed"), the REST approach is inefficient: it is better to use a message broker (Kafka, RabbitMQ).

#4. Problems with API versioning and evolution

Microservices often evolve independently, while REST contracts rigidly fix the data structure. Any change requires maintaining several API versions.

#5. Better alternatives for internal communication

• gRPC: a binary protocol, faster and more compact than JSON.
• Async messaging (Kafka, NATS, RabbitMQ): for event-driven systems.
• GraphQL or internal gateways: for aggregation and flexible queries.

Summary:

REST works well for external APIs, but is not always efficient for internal microservices, where speed, asynchrony, and loose coupling matter more.