System Design Series — Part 26

Imagine you're building an online food delivery platform like Swiggy or Zomato.

A customer places an order.

Behind the scenes, multiple services need to communicate:

• Order Service

• Payment Service

• Restaurant Service

• Delivery Service

• Notification Service

These services exchange thousands of requests every second.

Now imagine every request contains:

• Large JSON payloads

• HTTP headers

• Text serialization

As traffic grows, communication becomes slower.

Bandwidth increases.

Latency increases.

CPU usage increases.

Can services communicate faster?

Yes.

That's exactly why gRPC was created.

Let's understand it in the simplest way possible.

---

The Real Problem

Imagine your application has 50 microservices.

Every user action triggers communication between them.

Example:

User places an order.

↓

Order Service

↓

Payment Service

↓

Inventory Service

↓

Delivery Service

↓

Notification Service

If every service communicates using large JSON payloads,

millions of requests create unnecessary overhead.

Modern distributed systems need something faster.

---

A Simple Real-World Analogy

Imagine two friends talking.

REST API

One friend writes a complete letter.

The other reads it.

Then writes another letter.

The communication works.

But it's slow.

---

gRPC

Now imagine both friends are on a phone call.

They talk instantly.

No waiting.

No repeated introductions.

Communication becomes much faster.

That's exactly what gRPC offers.

---

What is gRPC?

gRPC stands for:

Google Remote Procedure Call

It is a high-performance communication framework developed by Google.

Unlike REST APIs,

gRPC focuses on:

• Speed

• Efficiency

• Low latency

It is widely used for communication between microservices.

---

How gRPC Works

Step 1

Client calls a remote method.

↓

Step 2

gRPC serializes data using Protocol Buffers.

↓

Step 3

HTTP/2 transports the request.

↓

Step 4

Server executes the method.

↓

Step 5

Binary response is returned.

Everything happens extremely quickly.

---

REST vs gRPC

REST

Uses:

HTTP

•  

JSON

Readable.

Easy to debug.

But larger payloads.

---

gRPC

Uses:

HTTP/2

•  

Protocol Buffers (Binary)

Smaller messages.

Faster communication.

Lower bandwidth usage.

---

What are Protocol Buffers?

Protocol Buffers (Protobuf) are Google's binary serialization format.

Instead of sending:

Large JSON text,

gRPC sends:

Compact binary data.

Benefits:

✔ Smaller payloads

✔ Faster serialization

✔ Lower network usage

This is one reason gRPC performs so well.

---

Why HTTP/2 Matters

Unlike HTTP/1.1,

HTTP/2 supports:

✔ Multiplexing

✔ Header Compression

✔ Persistent Connections

✔ Better Performance

Multiple requests can travel over the same connection simultaneously.

This significantly reduces latency.

---

Real-World Example

Imagine Netflix.

A user starts watching a movie.

Behind the scenes,

multiple services communicate:

Authentication

↓

Recommendation

↓

Playback

↓

Analytics

↓

Billing

These internal communications happen continuously.

Using lightweight binary messages makes the entire system faster.

---

Another Example: Uber

When you book a ride,

multiple backend services exchange information.

Examples:

Ride Matching

Pricing

Maps

Notifications

Payments

Thousands of service-to-service requests occur every second.

gRPC helps reduce communication overhead.

---

Types of gRPC Communication

One of the biggest advantages of gRPC is that it supports multiple communication patterns.

Unary

One request.

One response.

Similar to REST.

---

Server Streaming

Client sends one request.

Server streams multiple responses.

Example:

Live order tracking.

---

Client Streaming

Client sends multiple messages.

Server returns one response.

Useful for uploading large files.

---

Bidirectional Streaming

Both client and server exchange messages continuously.

Example:

Live multiplayer games.

Real-time collaboration.

IoT devices.

---

Production Architecture

Modern microservice architecture:

Users

↓

API Gateway

↓

REST APIs

↓

Microservices

↓

gRPC Communication

↓

Database

Notice:

External clients often use REST.

Internal microservices use gRPC.

This combination is very common in enterprise systems.

---

Why Companies Use gRPC

Large companies choose gRPC because it offers:

✔ Faster communication

✔ Lower bandwidth

✔ Better scalability

✔ Efficient service-to-service communication

It's especially valuable when thousands of internal API calls occur every second.

---

Advantages of gRPC

✔ Extremely fast

✔ Compact binary messages

✔ HTTP/2 support

✔ Strongly typed APIs

✔ Automatic client/server code generation

✔ Supports streaming

✔ Excellent for microservices

---

Challenges of gRPC

Harder to Test Manually

Unlike REST,

you can't simply open a browser and call an endpoint.

Specialized tools are often required.

---

Less Human Readable

Binary messages aren't as easy to inspect as JSON.

Debugging may require additional tooling.

---

Browser Limitations

Browsers don't directly support native gRPC.

Applications often use:

gRPC-Web

or

REST APIs for frontend communication.

---

Learning Curve

Teams need to understand:

• Protocol Buffers

• Code Generation

• Streaming

• HTTP/2

---

REST vs gRPC

Choose REST when:

✔ Public APIs

✔ Mobile apps

✔ Third-party integrations

✔ Simplicity is important

---

Choose gRPC when:

✔ Microservices communicate internally

✔ Performance matters

✔ Low latency is critical

✔ High throughput is required

Many production systems use both.

REST externally.

gRPC internally.

---

Common Developer Mistakes

Using gRPC for Every API

Not every application needs maximum performance.

---

Ignoring Browser Support

Frontend applications usually require REST or gRPC-Web.

---

Large Streaming Without Monitoring

Streaming connections consume resources.

Monitor them carefully.

---

Poor Protobuf Design

Well-designed contracts make APIs easier to evolve.

---

Production-Level Insight

A common misconception is:

"gRPC replaces REST."

It doesn't.

Most enterprise systems use:

REST

for client-facing APIs.

gRPC

for internal microservice communication.

Each technology solves a different problem.

The best architects understand where each one fits.

---

Interview Tip

A common System Design interview question is:

"When would you choose gRPC instead of REST?"

A strong answer should mention:

• Internal microservices

• Binary serialization

• Protocol Buffers

• HTTP/2

• Streaming

• Low latency

• High throughput

Interviewers want to know that you understand the trade-offs—not just the technology.

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Key Takeaways

✔ gRPC is a high-performance communication framework developed by Google

✔ It uses HTTP/2 and Protocol Buffers for fast, efficient communication

✔ Binary messages are smaller than JSON payloads

✔ gRPC supports unary and streaming communication

✔ It is widely used for internal microservice communication

✔ REST and gRPC often work together in modern architectures

✔ Choose the technology based on performance requirements and use cases

---

One of the biggest lessons in System Design is this:

As systems grow, the communication between services becomes just as important as the services themselves.

That's why many of the world's largest companies rely on gRPC to power high-performance distributed systems.

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This is Part 26 of the System Design Simplified series.

Next Article: Part 27 — API Versioning Explained Simply

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