What Is gRPC — A Protocol for High-Load Systems

When services in a distributed system exchange millions of messages per second, every extra byte and every millisecond of latency matters. It is precisely for such conditions that Google created gRPC — a remote procedure call framework that has become the de facto standard in the world of microservices. In this article, we will break down what gRPC is, how it works under the hood, how it differs from REST, and why blockchain infrastructure is already unthinkable without it.

What Is gRPC in Simple Terms

gRPC is an open-source framework for remote procedure calls (Remote Procedure Call). If you need to explain what gRPC is in simple terms, imagine that one service calls a function of another service as if it were part of its own code. The calling side does not worry about network transport, serialization, or routing — gRPC handles all of that.

The letter "g" in the name does not stand for "Google," although the company did indeed create gRPC based on the internal protocol Stubby, which had been used at Google since 2001. With each release, the "g" takes on a new meaning: good, green, glamorous. The project was open-sourced in 2015 and placed under the governance of the Cloud Native Computing Foundation (CNCF).

Key characteristics that define the gRPC protocol:

• Binary serialization via Protocol Buffers (Protobuf) instead of text-based JSON/XML.
• HTTP/2 as the transport protocol with stream multiplexing.
• Strict typing based on .proto files — the contract between client and server.
• Code generation of client and server stubs for 12+ programming languages.
• Four interaction modes: unary call, server streaming, client streaming, and bidirectional streaming.

gRPC is actively used in Kubernetes, Envoy, etcd, CockroachDB, as well as in blockchain nodes such as Cosmos SDK, Solana, Ethereum-compatible networks, and other Web3 infrastructure.

gRPC vs REST: Key Differences

Comparing gRPC and REST is one of the most discussed topics when choosing an architecture for inter-service communication. Both approaches solve the problem of communication between services, but they do so in fundamentally different ways.

Transport protocol. REST operates over HTTP/1.1 (although it can use HTTP/2), where each request opens a separate TCP connection or waits in a queue. gRPC is natively built on HTTP/2 with multiplexing — multiple requests are transmitted in parallel over a single TCP connection, eliminating the head-of-line blocking problem.

Data format. REST most commonly uses JSON — a human-readable but verbose format. The gRPC protocol uses Protobuf — a binary format that is 3-10 times more compact than JSON and significantly faster during serialization/deserialization. In Google's tests, a 50-byte Protobuf binary message corresponds to 200-300 bytes in JSON.

API contract. In REST, the specification is described via OpenAPI/Swagger, but adherence to it is up to the developers. In gRPC, the .proto file is the source code of the contract, from which the client and server are automatically generated. It is impossible to call a non-existent method or pass data of the wrong type — the error will occur at compile time.

Streaming. REST is limited to the request-response model. For real-time updates, you have to use WebSocket or Server-Sent Events — these are separate protocols with their own complexities. gRPC supports streaming natively, making it ideal for data streaming.

REST remains the better choice for public APIs consumed by browsers and mobile applications. gRPC wins where performance matters: internal microservices, IoT devices, real-time systems, and blockchain infrastructure.

How gRPC Works: Protocol Architecture

To gain a deeper understanding of what gRPC is as a technology, let us examine the protocol architecture layer by layer.

Service Definition in a .proto File

Everything starts with describing the service interface using the Protocol Buffers language:

syntax = "proto3";

service BlockchainNode {
  rpc GetBlock (BlockRequest) returns (BlockResponse);
  rpc StreamTransactions (FilterRequest) returns (stream Transaction);
}

message BlockRequest {
  uint64 block_number = 1;
  string chain_id = 2;
}

message BlockResponse {
  uint64 number = 1;
  string hash = 2;
  repeated Transaction transactions = 3;
  uint64 timestamp = 4;
}

From this file, the protoc compiler generates client and server code in the target language. The developer only needs to implement the business logic within the generated stubs.

Lifecycle of a Call

1. The client calls a method on the generated stub — a local object that looks like a regular function call.
2. The stub serializes the parameters via Protobuf into binary format.
3. The data is packed into an HTTP/2 frame with metadata (headers, deadline, tracing labels).
4. The server receives the frame, deserializes the message, and invokes the method implementation.
5. The response follows the reverse path: serialization, HTTP/2 frame, deserialization on the client.

The entire cycle for a unary call within a single data center takes fractions of a millisecond. At the same time, gRPC automatically manages the connection pool, retries, timeouts, and load balancing.

Metadata and Interceptors

gRPC supports transmitting metadata (analogous to HTTP headers) with each call. This allows implementing authentication, tracing, and rate-limiting without modifying business logic. Interceptors are middleware that processes each call before and after the main method executes.

Protobuf — The Data Format of gRPC

Protocol Buffers (Protobuf) is a serialization mechanism inseparably linked with gRPC. Although gRPC can theoretically work with JSON or FlatBuffers, Protobuf is used in the vast majority of cases.

Why Protobuf Is Faster Than JSON

JSON stores data in text form with field names: {"block_number": 12345678} — that is 27 bytes. Protobuf replaces field names with numeric tags and encodes values in a compact binary form. The same block number in Protobuf takes 5-6 bytes. The size savings are 3-10x, and parsing speed improves by 5-8x, because the binary format does not require lexical text parsing.

Backward Compatibility

One of Protobuf's strong points is its schema evolution mechanism. New fields are added with new tag numbers, and old clients simply ignore unknown fields. This is critically important in distributed systems where it is impossible to update all services simultaneously. In blockchain environments, where nodes run on different protocol versions, such compatibility is not a luxury — it is a necessity.

Limitations of Protobuf

Protobuf is not human-readable. Debugging requires utilities like grpcurl or Protobuf decoders. Additionally, .proto files need to be synchronized among all participants — this adds coordination overhead in large teams.

Streaming in gRPC: Four Interaction Modes

Streaming is one of the key advantages that makes gRPC something much more than just an alternative to REST. The framework supports four communication modes.

Unary call — the classic request-response model. The client sends one message and receives one response. Suitable for simple operations: fetching a block, checking a balance, requesting a transaction status.

Server streaming — the client sends one request, and the server responds with a stream of messages. An ideal scenario: subscribing to new blockchain blocks. The client makes one request — "subscribe to Ethereum blocks starting from number N" — and the server continuously delivers data about new blocks as they appear.

Client streaming — the client sends a stream of messages, and the server responds with a single message upon completion. Used for batch data uploads: for example, sending a batch of transactions for analysis.

Bidirectional streaming — both participants exchange message streams independently of each other. Used in complex scenarios: real-time state synchronization between nodes, interactive consensus protocols.

Example of a streaming service definition:

service NodeSync {
  // Bidirectional streaming for mempool synchronization
  rpc SyncMempool (stream MempoolEntry) returns (stream MempoolEntry);

  // Server streaming for event subscription
  rpc SubscribeEvents (EventFilter) returns (stream ChainEvent);
}

Unlike WebSocket, gRPC streaming is typed: at compile time, it is known which messages each side can send. This eliminates an entire class of errors related to mismatched formats.

gRPC in Blockchain Infrastructure

Blockchain infrastructure is an environment where the advantages of gRPC are fully realized. Every full node processes thousands of RPC requests per second: from dApps, wallets, indexers, bridges, and other services. The requirements for latency and throughput here are extreme.

Why Blockchain Nodes Choose gRPC

Cosmos SDK — one of the most popular frameworks for building blockchains — has used gRPC as its primary API since version 0.40. Solana provides a gRPC interface (Geyser) for streaming account and transaction updates in real time. The Ethereum ecosystem is moving in the same direction: the Firehose project by StreamingFast provides gRPC block streaming for EVM-compatible networks.

Reasons for the transition to gRPC in blockchain:

• Performance. JSON-RPC adds 30-50% serialization overhead. With millions of requests per day, this is a significant load on the node.
• Streaming subscriptions. Instead of polling via eth_getBlockByNumber every 2 seconds — a single gRPC stream that delivers blocks instantly.
• Strict contracts. .proto files guarantee that the client and the node speak the same language — no surprises with format changes.
• Multiplexing. A single TCP connection serves hundreds of parallel requests — critical when interacting with hundreds of dApps simultaneously.

The Role of gRPC Providers

Deploying and maintaining your own nodes is a resource-intensive task. This is exactly why infrastructure RPC providers exist, offering access to nodes via API. Settla, for example, works with gRPC endpoints for Cosmos-compatible networks and EVM chains, ensuring low latency and high node availability. For projects that need real-time blockchain data streaming, a gRPC connection through an infrastructure provider is the balance between performance and operational simplicity.

When to Use gRPC — and When Not To

The gRPC protocol is a powerful tool, but not a universal one. Here are clear criteria for making a decision.

gRPC Is the Right Choice When:

• Microservice architecture. Internal services communicate with each other through strictly typed contracts. gRPC delivers speed and reliability.
• High-load systems. If a service processes more than 10,000 requests per second, the savings on serialization and transport are noticeable.
• Real-time data streaming. Event subscriptions, metric streaming, blockchain data updates — gRPC streaming handles the task natively.
• Polyglot environment. Teams write in different languages (Go, Rust, Python, Java), but need a unified contract — a .proto file generates code for all of them.
• Blockchain infrastructure. Interacting with nodes, data indexing, RPC provisioning — it is the industry standard.

gRPC Is Not the Best Choice When:

• Public API for browsers. gRPC is not directly supported by browsers. gRPC-Web solves some of the problems but adds a proxy layer.
• Simple CRUD applications. If the service is a monolith with 5-10 endpoints, the overhead of .proto files and code generation is not justified.
• Human readability is required. For APIs tested via curl or Postman, JSON/REST is more convenient.
• HTTP-level caching. REST requests are easily cached by CDNs and proxies, while binary gRPC calls are not.

The Hybrid Approach

Many large platforms use both approaches: gRPC for internal communication between services and REST/GraphQL for the external API. An API gateway (Envoy, Kong, gRPC-Gateway) translates external REST requests into internal gRPC calls. This approach allows you to get the best of both worlds.

Practical Tips for Adopting gRPC

For those who have decided to integrate the gRPC protocol into their project, here are several practical recommendations.

Start with .proto files. Design your API in .proto first, then write the code. This is the contract-first approach, and it instills discipline.

Use deadlines. Every gRPC call should have a timeout. Without a deadline, a hung call will block resources indefinitely. In blockchain systems, where data becomes stale quickly, a deadline of 2-5 seconds is a reasonable value.

Configure retry policies. gRPC supports automatic retries for idempotent methods. Specify a retryPolicy in the service configuration so the client retries calls on transient errors.

Monitor with gRPC metrics. Interceptors allow you to collect latency, error, and load metrics for each method. Prometheus + Grafana is the standard stack for monitoring gRPC services.

Version your .proto files. Use versioned packages (package api.v1;) and never delete fields — mark them as reserved instead.

Conclusion

gRPC is not just a protocol — it is an entire ecosystem for building high-performance distributed systems. Binary serialization via Protobuf, HTTP/2 multiplexing, native streaming, and strict typing make it an indispensable tool for microservices, IoT, and blockchain infrastructure.

In the Web3 world, where the speed of access to blockchain data determines the competitiveness of a dApp, gRPC is becoming the standard. Infrastructure providers such as Settla offer gRPC access to nodes of major networks, allowing developers to focus on their product rather than on maintaining infrastructure.

If your project requires processing thousands of requests per second, streaming data, or communication between services written in different languages — gRPC deserves the top spot on your technology evaluation list.