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pc-book

I. Theory

  • RPC stands for Remote Procedure Calls It is a protocol allows a program to
    • execute a procedure of another program located in other computer.
    • without developer explicitly coding details for remote interaction

2. Stubs

  • gRPC needs stubs to communicate between services
  • Generate stubs:
    • first need API contract: contains services and payload messages in protocol buffered file
    • Why gRPC uses protocol buffer:
      • human-readable interface definition language (IDL)
      • automatically code generators for many languages
      • represent data in binary format:
        • smaller size
        • faster to transport
        • more efficient to serialize and deserialize than some text-based format like JSON or XML
      • strong typed-API contract between client and server which is super safe
      • conventions for API evolution
        • ensure backward and forward compatibility

3. HTTP/2

  • gRPC uses HTTP/2 as its transfer protocol
  • Great features gRPC inherits from HTTP/2:
    • binary framing:
      • more performance and robust
      • lighter to transport, safer to decode compare to other text-based protocol
      • great combination with protocol buffer
    • Header compression using HPACK:
      • reduce overhead and improve performance
    • multiplexing:
      • client and server can send multi requests and responses in parallel over a single TCP connection.
      • reduce latency and improve network utilization
    • allow server push:
      • one request from client, server can send back multi response -> valuable to reduce the round trip latency between client and server when server knows exactly what resources the client will be needed and send them before they are even requested

4. How HTTP/2 vs HTTP/1.1

HTTP/2 HTTP/1
Transfer Protocol Binary Text
Headers Compressed Plain text
Multiplexing Yes No
Requests per connections multiple 1
Server push Yes No

5. 4 types of gRPC

  1. Unary
  • client send 1 single request and server replies 1 single response. Similar to normal HTTP API.
  1. Client Streaming
  • client send stream of multi messages and expect server send back 1 single response.
  1. Server Streaming
  • client send 1 request message, server replies with a stream of multi messages
  1. Bidirectional Streaming
  • server and client keep send and receive multi messages in parallel with arbitrary order -> very complex, but flexible and no blocking -> no sides need to wait for the response before sending the next message.

6. gRPC vs REST

Feature gRPC REST
Protocol HTTP/2 (Fast) HTTP/1.1 (slow)
Payload Protobuf (binary, small) JSON (text, large)
API contract Strict, required to be clearly defined in .proto file Loose, optional (OpenAPI)
Code Generation Built-in in gRPC with helps of protocol buffer compiler Third-party tools like open API and swagger
Security TLS/SSL TLS/SSL
Streaming Bidirectional streaming Client -> server request only
Browser support Limited (require gRPC web with proxy layer to convert btw HTTP/1 and HTTP/2 fully supported by all browsers

7. Where gRPC is well suited to?

  • Micro-services is where gRPC shines
    • Low latency and high throughput communication.
    • Strong API contract.
  • Polyglot environments
    • gRPC provides code generation out of the box for many languages.
  • Point-to-Point communication
    • Excellent support for bidirectional streaming.
  • Network constrained environments- such as mobile app
    • Lightweight message format

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