How API Gateways Handle gRPC Requests

API7.ai

April 25, 2025

API Gateway Guide

Introduction

gRPC is a high-performance, open-source universal RPC framework that uses HTTP/2 for transport, Protocol Buffers for serialization, and supports streaming and multiplexing. It has gained significant traction in microservices and cloud-native architectures due to its speed and efficiency.

As more organizations adopt gRPC for inter-service communication, API gateways must evolve to handle gRPC requests effectively. This article explores how modern API gateways process, route, and manage gRPC traffic, what challenges they face, and what best practices developers should follow.

Understanding gRPC Basics

Before diving into how API gateways support gRPC, let's briefly review what makes gRPC unique:

  • Protocol: gRPC uses HTTP/2, allowing multiplexed streams over a single connection.
  • Message Format: Instead of JSON, gRPC uses Protocol Buffers (protobuf), a binary format that's compact and efficient.
  • Streaming: gRPC supports client-side, server-side, and bi-directional streaming.
  • Strong Typing: Protobuf enforces a schema-driven approach, enabling strict contracts.

These characteristics differ significantly from REST APIs and introduce new requirements for API gateways.

Why API Gateways Need to Support gRPC

API gateways traditionally focused on HTTP/1.1 and RESTful traffic. However, as gRPC adoption grows, there are several reasons why API gateways must support gRPC:

  • Unified Traffic Management: Consolidate observability, rate limiting, and authentication for both REST and gRPC.
  • Security Policies: Apply TLS termination, JWT validation, and role-based access control.
  • Routing Logic: Enable routing based on service names, method names, or headers.
  • Protocol Translation: In some cases, translate between REST and gRPC to support legacy clients.

Core Features Required for gRPC Support in API Gateways

1. HTTP/2 Support

  • Since gRPC runs on HTTP/2, gateways must support full-duplex streaming and connection multiplexing.
  • Gateways like Envoy, APISIX, and Kong natively support HTTP/2 and gRPC pass-through.

2. gRPC Routing and Load Balancing

  • Route requests based on gRPC service/method names.
  • Load balance based on method granularity, backend health, and metadata.

3. gRPC Transcoding

  • Convert gRPC to REST and vice versa using protocol translation.
  • Useful for exposing gRPC services to frontend clients or legacy systems.

4. Observability for gRPC

  • Extract gRPC metadata (method name, duration, status code) for logs, metrics, and traces.
  • Integrate with OpenTelemetry or Prometheus.

5. Authentication and Authorization

  • Apply OAuth2, JWT, and mTLS for securing gRPC traffic.
  • Ensure access policies can parse protobuf payloads when necessary.

Native gRPC Request Handling in API Gateway

sequenceDiagram
    participant Client
    participant API Gateway
    participant gRPC Service
    Client->>API Gateway: HTTP/2 gRPC Request
    API Gateway->>gRPC Service: Forward Request (no decoding)
    gRPC Service-->>API Gateway: gRPC Response
    API Gateway-->>Client: Forward gRPC Response

gRPC-JSON Transcoding via API Gateway

sequenceDiagram
    participant HTTP Client
    participant API Gateway
    participant gRPC Service
    HTTP Client->>API Gateway: HTTP/1.1 REST Request (JSON)
    API Gateway->>gRPC Service: Transcoded gRPC Request (protobuf)
    gRPC Service-->>API Gateway: gRPC Response (protobuf)
    API Gateway-->>HTTP Client: Transcoded JSON Response

Real-World Examples

Envoy

  • Native gRPC proxy with HTTP/2 and gRPC-Web support.
  • Supports RouteConfiguration using :method, :authority, and :path headers.
  • Supports gRPC-JSON transcoding via proto_descriptor.

Apache APISIX

  • gRPC support with gRPC proxy plugin.
  • TLS termination, mTLS authentication, and routing using URI and host.
  • Integrates with Prometheus and SkyWalking for gRPC observability.

Kong

  • HTTP/2 and gRPC proxying.
  • Authentication plugins (e.g., JWT) work for gRPC with content-type: application/grpc.
  • OpenTelemetry plugin supports gRPC spans.

Best Practices for gRPC at the Gateway

  • Use native HTTP/2 support in gateways to avoid compatibility issues.
  • Monitor gRPC-specific metrics, like streaming duration and method latency.
  • Keep proto descriptors up to date when using gRPC transcoding.
  • Secure transport with mTLS especially for internal microservice traffic.
  • Consider gRPC-Web for browser compatibility.

Challenges and Considerations

  • Limited browser support for gRPC; gRPC-Web mitigates this.
  • Complex debugging due to binary protocol (protobuf).
  • Header size limits and connection reuse must be tuned for streaming workloads.
  • Tooling and observability are less mature compared to REST.

Conclusion

As gRPC continues to shape the landscape of microservice communication, API gateways must provide first-class support for this protocol. From handling HTTP/2 and streaming to enabling protocol translation and enforcing security, modern gateways play a critical role in making gRPC manageable at scale.

When choosing or configuring an API gateway for gRPC, it is crucial to understand both the protocol's capabilities and the gateway's feature set. With the right setup, developers can harness the performance benefits of gRPC while maintaining control, security, and observability across their services.

FAQ

1. What is gRPC and how does it differ from REST?

gRPC is a high-performance RPC framework using HTTP/2 and protobuf. It enables binary messaging, bi-directional streaming, and strong typing—unlike REST which relies on HTTP/1.1 and JSON.

2. Can API gateways convert REST to gRPC?

Yes. Gateways like Envoy and APISIX support gRPC-JSON transcoding to translate RESTful HTTP requests into gRPC calls.

3. Is gRPC secure?

gRPC supports TLS and mutual TLS (mTLS) for encryption and authentication. API gateways can enforce additional security policies.

4. Do all API gateways support gRPC?

No. Support varies. Envoy, Kong, and APISIX offer strong gRPC support. NGINX requires additional configuration or third-party modules.

5. What about browser support for gRPC?

Browsers don't natively support HTTP/2 framing required by gRPC. Use gRPC-Web to bridge the gap.

Next Steps

Stay tuned for our upcoming column on the API gateway Guide, where you'll find the latest updates and insights!

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