What is RPC (Remote Procedure Call)?

What is RPC (Remote Procedure Call)?

Remote Procedure Call (RPC) is a protocol that allows a computer program to execute a function or procedure on another computer (remote server) as if it were a local function.

Key Idea: RPC enables communication between different processes across a network or within the same system.
Used In: Microservices, Distributed Systems, API Communication, Cloud Computing.

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How Does RPC Work?

Client sends a request → Calls a function on a remote server.
Server processes the request → Executes the function.
Server sends a response → Returns the output to the client.

Example of RPC Flow:

Client App  ── Request (RPC Call) ──> Remote Server  
Remote Server  ── Process & Execute ──> Send Response  
Client App  ── Receive & Process Response ──> Done 

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Types of RPC

Synchronous RPC

• Client waits for the server to respond before continuing.
• Example: Traditional API calls (like REST).

Asynchronous RPC

• Client does not wait for a response, allowing parallel execution.
• Example: Event-driven microservices.

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RPC vs. REST API

Feature	RPC	REST API
Protocol	Can use HTTP, TCP, UDP, gRPC, etc.	Uses HTTP
Data Format	Binary (Protocol Buffers, Thrift, Avro) or Text (JSON, XML)	JSON/XML
Performance	Faster (Binary format + Compression)	Slower due to HTTP overhead
Streaming Support	Yes (gRPC, Thrift, WebSockets)	Limited (Needs WebSockets)
Use Case	Microservices, High-Performance APIs	Web & Mobile APIs

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Popular RPC Frameworks

RPC Framework	Used For	Protocol
gRPC	Microservices, Cloud APIs	HTTP/2 + Protocol Buffers
Apache Thrift	High-speed RPCs	Binary Protocol, TCP
JSON-RPC	Web APIs	HTTP + JSON
XML-RPC	Legacy systems	HTTP + XML

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Example of RPC Call

Using gRPC (Google RPC) in Python:

import grpc
import example_pb2
import example_pb2_grpc

channel = grpc.insecure_channel('localhost:50051')
stub = example_pb2_grpc.GreeterStub(channel)
response = stub.SayHello(example_pb2.HelloRequest(name='Alice'))
print(response.message)

This sends an RPC request to a server and gets a response.

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When to Use RPC?

When high-speed communication is needed (Microservices, Cloud).
When APIs must support streaming & multiplexing (gRPC).
When services need to communicate in different programming languages.

What is an RPC Framework?

What is an RPC Framework?

An RPC (Remote Procedure Call) framework is a set of tools, libraries, and protocols that allow applications to execute functions or procedures on a remote server as if they were local functions.

Purpose: Simplifies communication between distributed systems, microservices, and cloud applications.
Example Use Case: A frontend app calling a backend function on a remote server without worrying about networking details.

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How Does an RPC Framework Work?

Client makes an RPC request (calls a function remotely).
RPC framework serializes the request (converts data into a transportable format).
Server receives and processes the request.
RPC framework deserializes the response and returns it to the client.

Example of an RPC Call Flow:

Client  ──> RPC Framework ──> Network ──> Server  
Client  <── RPC Framework <── Network <── Server Response

Think of it like calling a function, but it runs on another server!

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Popular RPC Frameworks

RPC Framework	Used For	Protocol	Serialization Format
gRPC	Microservices, Cloud APIs	HTTP/2	Protocol Buffers (ProtoBuf)
Apache Thrift	Cross-language RPC	TCP, HTTP	Compact Binary Format
JSON-RPC	Web APIs, JavaScript-based Apps	HTTP, WebSockets	JSON
XML-RPC	Legacy Systems	HTTP	XML
ZeroMQ (ØMQ)	High-performance messaging	Custom (No built-in protocol)	Custom
Dapr	Cloud-Native Applications	HTTP/gRPC	JSON/ProtoBuf

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Why Use an RPC Framework?

Simplicity → Developers call remote functions like local functions.
High Performance → Many frameworks (like gRPC) use binary serialization for fast data transmission.
Cross-Language Support → Works across different programming languages (e.g., Python client calling a Go server).
Streaming Support → Some frameworks (e.g., gRPC) support bidirectional streaming.

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gRPC Example (Python)

Define an RPC Service (hello.proto):

syntax = "proto3";

service Greeter {
  rpc SayHello (HelloRequest) returns (HelloReply);
}

message HelloRequest {
  string name = 1;
}

message HelloReply {
  string message = 1;
}

The RPC framework handles serialization, networking, and responses automatically!

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Final Thoughts

An RPC framework helps build high-performance distributed systems efficiently!
Best for: Microservices, Cloud APIs, and High-Speed Communication.
Best choice: gRPC for modern systems, Thrift for cross-language, and JSON-RPC for web apps.

Difference Between RPC and RPC Framework

Aspect	RPC (Remote Procedure Call)	RPC Framework
Definition	A concept that allows calling functions on a remote server as if they were local.	A set of tools, libraries, and protocols that implement RPC functionality.
Functionality	Enables communication between client and server in distributed systems.	Provides ready-to-use implementations for handling RPC calls, serialization, security, and networking.
Example Concept	A client requests a function (getUserDetails()) on a remote server.	A framework like gRPC, Apache Thrift, or JSON-RPC handles the networking, serialization, and execution of getUserDetails().
Transport Mechanism	Can work over HTTP, TCP, UDP, WebSockets, etc.	Uses specific transport mechanisms like HTTP/2 (gRPC), TCP (Thrift), or HTTP (JSON-RPC).
Serialization	Requires a way to encode and decode data (e.g., JSON, XML, Binary).	Built-in serialization formats like ProtoBuf (gRPC), JSON (JSON-RPC), or Binary (Thrift).
Security	Must be implemented separately (e.g., authentication, encryption).	Many frameworks provide built-in TLS encryption, authentication, and access control.
Cross-Language Support	Requires manual implementation for different languages.	Provides auto-generated client and server code for multiple languages (e.g., Python, Java, Go, C++).

How RPC Works (Conceptually)?

Client Calls a Function

• A client program calls a function (getUserDetails()) that is actually located on a remote server.

Request Serialization

• The function call’s parameters (data) are converted into a format that can be transmitted over a network (e.g., JSON, Protocol Buffers, XML, Binary).

Network Transmission

• The serialized data is sent over a network (via HTTP, TCP, UDP, WebSockets, etc.).

Server Receives the Request

• The server’s RPC system deserializes the request and calls the actual function on the server.

Function Execution & Response

• The server executes the function (getUserDetails()) and sends the response back to the client.

Client Receives the Response

• The client deserializes the response and continues execution as if the function ran locally.

RPC Conceptual Flow:

pgsqlCopyEditClient ───> (Serialize Data) ───> Network ───> Server  
Server ───> (Execute Function) ───> Return Response ───> Client  

RPC vs. Normal Function Calls

Feature	Local Function Call	Remote Procedure Call (RPC)
Execution Location	Runs on the same machine	Runs on a remote server
Data Passing	Direct memory access	Data is serialized and sent over the network
Performance	Fast (no network delay)	Slower (network latency)
Complexity	Simple	Requires handling network failures, serialization, security
Use Case	Local programs	Microservices, Cloud APIs, Distributed Systems

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Real-World Use Cases of RPC

Microservices Communication → Services talk to each other in cloud-native applications.
Database Requests → Clients call database functions remotely.
Remote System Administration → Commands are executed on remote servers.
Game Servers & Multiplayer Apps → Actions from one player affect other players over a network.

List of All Popular RPC Frameworks

RPC frameworks simplify remote function execution by handling networking, serialization, and security. Below is a list of widely used RPC frameworks categorized based on their use cases.

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Modern High-Performance RPC Frameworks

Framework	Description	Protocol	Serialization Format	Best For
gRPC	Google’s high-performance RPC framework	HTTP/2	Protocol Buffers (ProtoBuf)	Microservices, Cloud APIs
Apache Thrift	Cross-language RPC system	TCP, HTTP	Compact Binary, JSON, Simple JSON	Large-scale distributed systems
Cap’n Proto	High-speed serialization and RPC	Custom (No extra encoding needed)	Cap’n Proto (Zero Parsing Overhead)	Low-latency systems
Dapr	Cloud-native distributed application runtime	HTTP, gRPC	JSON, ProtoBuf	Microservices & Kubernetes

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Web-Based RPC Frameworks

Framework	Description	Protocol	Serialization Format	Best For
JSON-RPC	Lightweight RPC using JSON over HTTP/WebSockets	HTTP, WebSockets	JSON	Web applications, JavaScript-based systems
XML-RPC	Simple RPC protocol using XML over HTTP	HTTP	XML	Legacy systems
WAMP (Web Application Messaging Protocol)	Web-based RPC with real-time pub/sub	WebSockets, TCP	JSON, MsgPack, CBOR	WebSockets-based APIs
Falcor	Netflix’s RPC for efficient data fetching	HTTP	JSON	Web applications

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Messaging-Based RPC Frameworks

Framework	Description	Protocol	Serialization Format	Best For
ZeroMQ (ØMQ)	High-performance messaging library	TCP, IPC, Multicast	Custom	Low-latency, real-time systems
Apache Avro	Schema-based RPC with a focus on Big Data	TCP, HTTP	Avro Binary, JSON	Big Data, Streaming (Kafka, Hadoop)
MessagePack-RPC	Lightweight binary-based RPC	TCP, UDP	MessagePack	IoT & high-performance applications
Nanomsg	Simplified version of ZeroMQ	TCP, IPC	Custom	High-speed messaging

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Enterprise & Legacy RPC Frameworks

Framework	Description	Protocol	Serialization Format	Best For
CORBA (Common Object Request Broker Architecture)	Classic RPC framework for enterprise systems	IIOP (TCP-based)	Binary (IDL-based)	Legacy enterprise applications
RMI (Remote Method Invocation)	Java’s built-in RPC mechanism	JRMP (Java Remote Method Protocol)	Java Serialization	Java-based distributed applications
Hessian	Lightweight binary-based RPC	HTTP	Hessian Binary Format	Java & cross-platform systems
TARS	Tencent’s distributed RPC framework	TCP, HTTP	TARS, ProtoBuf, JSON	Large-scale microservices

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Blockchain & Decentralized RPC Frameworks

Framework	Description	Protocol	Serialization Format	Best For
Ethereum JSON-RPC	RPC API for Ethereum blockchain	HTTP, WebSockets	JSON	Blockchain applications
Bitcoin RPC	RPC interface for Bitcoin nodes	HTTP	JSON	Cryptocurrency development

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Choosing the Right RPC Framework

Use Case	Recommended Framework
Microservices & Cloud	gRPC, Thrift, Dapr
Web-Based RPC	JSON-RPC, WAMP, Falcor
Big Data & Streaming	Apache Avro, MessagePack-RPC
Low-Latency & High-Performance	ZeroMQ, Cap’n Proto
Enterprise & Legacy Apps	CORBA, RMI, Hessian
Blockchain Apps	Ethereum JSON-RPC, Bitcoin RPC

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Final Thoughts

If you need a high-performance modern RPC framework, use gRPC or Apache Thrift.
For web-based applications, JSON-RPC is a lightweight option.
For low-latency, high-speed messaging, ZeroMQ or Cap’n Proto are great choices.
For distributed systems and big data, Apache Avro is recommended.

Default RPC Methods in Different Scenarios

Below is a breakdown of what happens by default when you call a remote function in different environments.

Scenario	What Happens By Default?	Default RPC Framework
PHP in XAMPP (Apache Server)	No native RPC; you must use JSON-RPC, SOAP, or REST	None (you must specify)
Java Calling Remote Functions	Uses Java RMI (Remote Method Invocation)	Java RMI
Python Calling a Remote Function	Uses built-in xmlrpc.client for XML-RPC	XML-RPC
Node.js Communicating with Remote Services	Typically uses HTTP API calls (REST)	HTTP (REST)
.NET / C# Calling Remote Services	Uses WCF (Windows Communication Foundation)	WCF (SOAP/XML-RPC)
C++ Distributed Systems	Uses CORBA (Common Object Request Broker Architecture)	CORBA
Web Browsers Calling Remote Functions	Uses AJAX (JavaScript HTTP Requests)	REST over HTTP (AJAX, Fetch API)
Linux System Calls	Uses gRPC or DBus for inter-process communication	gRPC, DBus
Blockchain Smart Contracts (Ethereum, Bitcoin, etc.)	Uses JSON-RPC to communicate with nodes	JSON-RPC