Demo 05 — REST vs gRPC: Two Protocols

One Spring Boot app simultaneously serves REST on :8080 and gRPC on :9000. Same service, two protocols, honest comparison including the localhost caveat.

Spring Boot 4.0 gRPC support

Spring Boot 4.0 introduces first-class gRPC support via spring-grpc-spring-boot-starter. No third-party libraries needed.

<dependency>
    <groupId>org.springframework.grpc</groupId>
    <artifactId>spring-grpc-spring-boot-starter</artifactId>
</dependency>

# application.yml
spring:
  grpc:
    server:
      port: 9000

The honest localhost caveat

gRPC unary is slower than REST on localhost. Network cost is zero on loopback. gRPC’s advantages only materialise with real pod-to-pod network latency.

What gRPC wins even on localhost:

• Server streaming: 1 connection vs 1,000 REST requests
• High concurrency (c=500): HTTP/2 multiplexing vs 500 TCP connections

In production (pod-to-pod): gRPC wins ~3-4x throughput, ~73% p50 latency.

Streaming modes

# Live stream — one push per second (count=0)
grpcurl -plaintext -d '{"host":"localhost","count":0}' \
  localhost:9000 MetricsService/StreamMetrics

# Benchmark — 1000 messages as fast as possible
grpcurl -plaintext -d '{"host":"localhost","count":1000}' \
  localhost:9000 MetricsService/StreamMetrics

Prerequisites

hey, grpcurl, ghz — see Prerequisites guide.

Reference

• Demo source
• Spring gRPC documentation