PubSub at Rails - Speaker Deck

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PubSub in Rails @just_lest

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Real-time features

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Real-time features → Collaboration → Asynchronous tasks → Keeping UI in sync

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Action Cable Action Cable seamlessly integrates WebSockets with the rest of your Rails application. http://guides.rubyonrails.org/ action_cable_overview.html

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Besides WebSocket protocol → Polling → Long-polling → EventSource

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WebSocket protocol → Full-duplex → Low overhead

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WebSocket protocol var socket = new WebSocket('ws://www.example.com/socketserver') socket.onopen = function () { websocket.send('Hello') } socket.onmessage = function (msg) { console.log(msg) }

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Action Cable ApplicationCable::Connection is a WebSocket connection ApplicationCable::Channel is a unit of work inside a connection

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Action Cable Action Cable uses Pub/Sub to communicate between the server and many clients. http://guides.rubyonrails.org/ action_cable_overview.html

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What is PubSub?

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What is PubSub? → Publishers → Subscribers

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Message reliability

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Losing messages → Flaky internet connection → Swithing Wi-Fi networks → Closing your laptop's lid

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Message reliability Messaging reliability is far more important than WebSockets. WebSockets are an implementation detail, not a feature. Sam Saffron https://samsaffron.com/archive/2015/12/29/ websockets-caution-required

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Message reliability Twitter use HTTP/2 + polling, Facebook and Gmail use Long Polling. Sam Saffron https://samsaffron.com/archive/2015/12/29/ websockets-caution-required

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HTTP/2

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HTTP/2 There is no websockets for HTTP/2. By this, I mean that there’s no way to negotiate or upgrade a connection to websockets over HTTP/2 like there is for HTTP/1.1 as expressed by RFC 6455. Daniel Stenberg https://daniel.haxx.se/blog/2016/06/15/no- websockets-over-http2/

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HTTP/2 Open 20 tabs with a WebSocket based application and you are risking 20 connections unless the client/server mitigates. Sam Saffron https://samsaffron.com/archive/2015/12/29/ websockets-caution-required

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HTTP/2 HTTP comes with a lot of goodies, and by moving away from HTTP we'll lose it all. Caching, routing, multiplexing, gzipping and lot more. You could reimplement all of these things in Action Cable, but why? Nate Berkopec https://www.nateberkopec.com/2015/09/30/action- cable.html

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Possible issues → Proxies when using unsecured HTTP → Load balancing

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What to do then?

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message_bus A reliable, robust messaging bus for Ruby processes and web clients. https://github.com/SamSaffron/message_bus

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message_bus https://www.discourse.org

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message_bus → Provides reliable queue → Supports both server-to-client and server-to- server communication

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message_bus → Long-polling with chunked encoding (streaming) → Long-polling → Polling

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But when to use WebSockets? → To utilize full-duplex connection → To minimize latency and overhead

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Thank you!