Remote Procedural Call (RPC) Mechanism

A Remote Procedure Call (RPC) is a communication protocol that enables a program to request a service or execute a procedure on a remote server as though it were a local function call.

• The client invokes a function on the server located in a different address space.
• The RPC framework handles the details of network communication, serialization, and response management.
• This makes remote communication transparent to developers, promoting cleaner and more modular distributed applications.

Importance of RPC in Distributed Systems

Simplified Communication

• Abstraction of complexity: Developers call remote services as if they were local methods.
• Consistent interface: Uniform way of invoking services across the system.

Enhanced Modularity and Reusability

• Decoupling: System components interact without being tightly coupled.
• Reusability: Remote services can be reused across multiple applications.

Facilitates Distributed Computing

• Inter-Process Communication (IPC): Enables different processes on different machines to collaborate.
• Resource Sharing: Allows sharing of resources like databases, computing power, or specialized services.

RPC Architecture in Distributed Systems

RPC follows a client-server model, where the client requests execution of a remote procedure and the server responds.

1. Client and Server Components

• Client: Initiates the request using a local stub.
• Server: Hosts the actual implementation of the remote procedure.

2. Stubs

• Client Stub: Packs (marshals) arguments, sends request, and receives results.
• Server Stub: Unpacks (unmarshals) arguments, executes the procedure, and sends results back.

3. Marshalling and Unmarshalling

• Marshalling: Converts data/arguments into transmittable byte streams.
• Unmarshalling: Converts byte streams back into usable data.

4. Communication Layer

• Uses transport protocols (TCP/UDP).
• Manages message routing, buffering, and error handling.

5. RPC Framework

• IDL (Interface Definition Language): Defines procedures, parameters, and return types independent of programming language.
• RPC Protocol: Specifies communication rules, request-response format, and error handling.

6. Error Handling and Fault Tolerance

• Timeouts and Retries: To handle failures and delays.
• Exception Handling: Reports errors to clients.

7. Security

• Authentication/Authorization: Ensures only valid clients can access services.
• Encryption: Protects data during transmission (e.g., SSL/TLS).

Types of RPC

1. Synchronous RPC

• Client waits for server response.
• Simple design but blocking in nature.
• Used when immediate response is required.

2. Asynchronous RPC

• Client sends request and continues execution without waiting.
• More complex but improves responsiveness.
• Used in concurrent applications.

3. One-Way RPC

• Client sends request without expecting any response.
• "Fire-and-forget" style.
• Used in logging or notification services.

4. Callback RPC

• Server invokes a client-provided callback after processing.
• Useful for long-running operations.

5. Batch RPC

• Multiple requests are bundled into one batch.
• Reduces network round trips and overhead.