backend-and-orchestration-toolkit/resources/protocols

🪡 Protocols

What's a protocol

• a protocol is a system that allows two parties to communicate
• they are designed with a set of properties, depending on their purpose

Protocol design properties

• data format
  • text based (plain text, JSON, XML)
  • binary (protobuf, RESP, h2, h3)
• transfer mode
  • message based (UDP, HTTP)
  • stream (TCP, WebRTC)
• addressing system
  • DNS name, IP, MAC
• directionality
  • bidirectional (TCP)
  • unidirectional (HTTP)
  • full/half duplex
• state
  • stateful
  • stateless
• routing
  • proxies, gateways

Why do you need a communication model?

• you want to build agnostic applications
• without a standard model, upgrading network equipments become difficult
• innovations can be done in each layer separately without affecting the rest of the models
• the OSI model is 7 layers, each describing a specific networking component

What's the OSI model?

• layer 7, application: HTTP, FTP, gRCP
• layer 6, presentation: encoding, serialization
• layer 5, session: connection establishment, TLS
• layer 4, transport: UDP, TCP
• layer 3, network: IP
• layer 2, data link: frames, mac address ethernet
• layer 1, physical: electric signals, fiber or radio waves

An example sending a POST request

• layer 7: POST request with JSON data to HTTP server
• layer 6: serialize JSON to flat byte strings
• layer 5: request to establish TCP connection/TLS
• layer 4: send SYN request target port 443
• layer 3: SYN is placed an IP packet(s) and adds the source/dest IPs
• layer 2: each packet goes into a single frame and adds the source/dest MAC addresses
• layer 1: each frame becomes a string of bits which converted into either radio signal (wifi), electric signal (ethernet), or light (fiber)

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HTTP/1.1, 2, 3

• clients example: browser, apps that make http request
• server examples: IIS, Apache TomCat, Python Tornado, NodeJS

What's an HTTP request

• a method (GET, POST, etc.)
• a path (the URL)
• a protocol (HTTP/1.1, 2, 3 etc.)
• headers (key-values)
• body

HTTP/2

• by google, called SPDY
• support compression in both head and body
• multiplexing
• server push
• secure by default
• protocol negotiation during TLS (NPN/ALPN)

HTTP/3

• HTTP over QUIC and multiplexed streams over UDP
• merges connection setup + TLS in one handshake
• has congestion control at stream level

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WebSockets (ws://, wss://)

• bidirectional communications on the web
• use cases: chatting, live feed, multiplayer gaming, showing client progress/logging
• apps: twitch, whatsapp
• pros: full-duplex (no polling), http compatible, firewall friendly
• cons: proxying is tricky, layer 7 load balancing is challenging (timeouts), stateful and difficult to horizontally scale
• long polling and side server events might be better solutions

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gRPC

• built on top of HTTP/2 (as a hidden implementation), adding several features
• any communication protocol needs client library for the language of choice, but with gRPC you only have one client library
• message format is protocol buffers
• the gRPC modes are: unary, server streaming, client streaming, and bidirectional streaming
• pros: fast and compact, one client library, progress feedback (upload), cancel request (H2), H2/protobuf
• cons: schema, thick client (libraries have bugs), proxies, no native error handling, no native browser support, timeouts (pub/sub)

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WebRTC (web real-time communication)

• find a p2p path to exchange video and audio in an efficient and low-latency manner
• standardized API
• enables rich communication browsers, mobile, IOT devices
• pros: p2p is great (low latency for high bandwidth content), standardized api
• cons: maintaining STUN and TURN servers, p2p falls apart in case of multiple participants (e.g., discord)

WebRTC overview

1. A wants to connect to B
2. A finds out all possible ways the public can connect to it
3. B finds out all possible ways the public can connect to it
4. A and B signal this session information via other means (whatsapp, QR, tweet, etc.)
5. A connects to B via the most optimal path
6. A and B also exchange their supported media and security

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Proxies

What's a proxy

• a server that makes requests on your behalf (you as a client)
• this means that your tcp connection is being established not with the server, but with the proxy
• in other words, the proxy has the role of layer 4, but layer 7 content gets forwarded (there are exceptions when the proxy adds a header such as with X-Forwarded-For)
• uses: caching, anonymity, logging, block sites, microservices

What's a reverse proxy

• the client does not know the "final destination server", meaning that the server thar serves the url requested could be a reverse proxy that will forward the request to the underline server
• uses: load balancing, caching, CDN, api gateway/ingress, canary deployment, microservices

Layer 4 vs. Layer 7 Load Balancers

• load balancers, also known as fault tolerant systems, is a reverse proxy talking to many backends
• a layer 4 load balancer starts with several TCP connection and keep them "warm"
  • when a user starts a connection, this connection will have a state, the LB chooses one server and all segments for that connection go to that server and through ONE connection (layer 4 is stateful)
  • the LB almost acts like a router
  • pros: simpler load balancing, efficient, more secure, works with any protocol, one TCP connection (NAT)
  • cons: no smart load balancing, NA services, sticky per connection, no caching, protocol unaware (can be risky) bypass rules
• a layer 7 load balancer starts with several TCP connection and keep them "warm", but in this case, when a client connects to the L7 LB, it becomes protocol specific
  • any logical request will be buffered, parsed, and then forwarded to a new backend server
  • this could be one or more segments
  • certificates, private keys, all need to live in the load balancer
  • pros: smart LB, caching, great for microservices, API gateway logic, authentication
  • cons: expensive (because it's looking at the data), decrypts (terminates TLS), two TCP connections, needs to buffer, needs to understand protocol