Kafka vs REST

 

REST API = synchronous request-response communication.

Kafka = asynchronous event streaming/message broker.

Throughput

Suppose you need to process 100,000 transactions per second.

REST

Every request:

• Opens/uses connection
• Executes logic
• Returns response

The API server becomes the bottleneck.

Kafka

Messages are:

• Batched
• Sequentially written to disk
• Consumed independently

Kafka is designed for extremely high throughput.

Winner for throughput:

✅ Kafka

Example:

• Website clickstream events
• Telemetry data
• IoT sensor data
• Log aggregation

Scalability

REST

Scaling often means:

• More API instances
• Load balancers
• Database scaling

All consumers hit the same API.

Kafka

You can independently scale:

• Producers
• Brokers
• Consumer groups

If traffic doubles:

• Add more consumers
• Rebalance partitions

Winner:

✅ Kafka

Reliability Under Load

REST

If a downstream service is unavailable:

• Requests timeout
• Retries increase load
• Cascading failures may occur

Kafka

Messages remain in the broker:

• Consumers can be offline
• Processing resumes later
• No message loss (with proper configuration)

Winner:

✅ Kafka

Fan-Out Performance

Suppose an order event must be consumed by:

• Billing service
• Inventory service
• Analytics service
• Notification service

REST

Order Service
    |
    |--> Billing API
    |--> Inventory API
    |--> Analytics API
    |--> Notification API

Many network calls.

Kafka

Order Service --> Kafka Topic

Billing Consumer
Inventory Consumer
Analytics Consumer
Notification Consumer

Single publish, many consumers.

Winner:

✅ Kafka

Resource Usage

REST

Good for:

• Interactive user operations
• CRUD applications
• Real-time queries

Kafka

Good for:

• Massive event streams
• Decoupled microservices
• Event sourcing
• Data pipelines

Aspect	REST API	Kafka
Communication	Synchronous	Asynchronous
Latency	Very low (milliseconds) for direct request	Slightly higher end-to-end due to broker hop
Throughput	Limited by API server capacity	Extremely high (millions of messages/sec possible)
Scalability	Scale API servers horizontally	Scale producers, brokers, and consumers independently
Reliability	Client retries required	Built-in persistence and replay
Backpressure handling	Difficult	Native consumer lag handling
Fan-out to multiple consumers	Multiple API calls needed	Publish once, consume many times
Real-time response	Excellent	Not ideal for immediate response