Why Elixir?

Why Elixir? Isn’t that just Erlang? And isn’t Erlang weird?

Elixir brings modern accessibility to the venerable Erlang VM. For years the weirdness of Erlang syntax has overshadowed the robustness and scalability of the underlying system. As demand for realtime web experiences has grown, the unmatched ability of an Erlang application to handle concurrent user interactions at scale is coming into its own. You’ve heard the legends of 15 WhatsApp engineers handling 500 million users thanks to Erlang. We’ll look at examples of Elixir’s expressive syntax making short work of typical problems like sending emails in the background, what it takes to give everyone on Earth their own websocket connection, and how functional programming makes it all possible.

Transcript

1. Why Elixir? Saturday, May 20 2017 Desmond Bowe n languages May 11, 2017
2. • 7 years professional experience • 2 years Elixir experience • Principal at Crevalle • Founder of EMPEX • Pinball enthusiast
3. A few dozen users.
4. A few dozen users.
5. Elixir
6. Elixir new syntax for Erlang
7. Syntax defmodule Crevalle do def sweet_function(input) do String.replace(input, "\n", ",") end end basic function calls
8. Syntax string interpolation defmodule Crevalle do def interpolate(str) do "you gave me #{str}" end end
9. Syntax function pattern matching defmodule Crevalle do def welcome("Harriet") do "You're my favorite!" end def welcome("Susan") do "oh, hey, I guess" end end Crevalle.welcome("Harriet") # => "You're my favorite!" Crevalle.welcome("Susan") # => ...
10. Syntax function argument destructuring defmodule Crevalle do def welcome(%{"Harriet" => %{"age" => age}}) do "Congratulations on being #{age}" end def welcome(%{"Harriet" => _attrs}) do "We're not sure how old you are" end def welcome(_) do "Who is this? What's your identification?" end end Crevalle.welcome(%{"Harriet" => %{"age" => 42}}) # => "Congratulations..." Crevalle.welcome(%{"Harriet" => %{"eyes" => "blue"}}) # => "We're not sure..." Crevalle.welcome(%{"Susan" => %{"shoe_size" => 8}}) # => "Who is this?"
11. Syntax do away with if statements defmodule Crevalle do def age(years) when years < 25 do "You could still be bad." end def age(years) when years > 25 do "Too invested in the system." end end Crevalle.age(23) # => "You could still be bad." Crevalle.age(31) # => "Too invested in the system." Crevalle.age(25) # => ** (UndefinedFunctionError) function Crevalle.age/1 is undefined or private.
12. Syntax passing similarity to Ruby
13. Syntax passing similarity to Ruby
14. Erlang VM
15. Erlang VM Processes • Cheap: ~2kb memory overhead • Plentiful: default max 32,768, up to millions, limited by RAM • Isolated: independent stack, GC spawn a process → supervise it → send it messages → save/retrieve state
16. Erlang VM BEAM OS RUN QUEUE process process process SCHEDULER CPU Fair Scheduling Processes don’t block each other, even during I/O
17. Erlang VM BEAM OS RUN QUEUE process process process SCHEDULER CPU Concurrent Computations RUN QUEUE process process process SCHEDULER CPU
18. GenServer
19. GenServer what’s a GenServer? • Long-Running process • Uses client/server semantics (picoservice) • Send it messages, it does stuff, sometimes returns an answer • Basically a recursive receive loop, constantly checking for messages • Plus bells and whistles
20. GenServer defmodule Lily.WeeklyCompletedEmail do use GenServer def start_link do GenServer.start_link(__MODULE__, :ok, name: __MODULE__) end def init(:ok) do Process.send_after(self(), :send_email, time_until_sunday_evening()) {:ok, %{items: []} end def handle_info(:send_email, state) do items = Lily.WeeklySummary.this_week Lily.Mailer.send_weekly_completed_email("desmond@crevalle.io", items) Process.send_after(self(), :send_email, seven_days_from_now()) new_state = Map.put(state, :items, items) {:noreply, new_state} end def seven_days_from_now, do: 86_400 * 7 def time_until_sunday_evening, do: DateTime.time_until_sunday_evening() end
21. Other kinds of process spawning def handle_info(:send_email, state) do items = Lily.WeeklySummary.this_week Task.async(fn -> Lily.Mailer.send_weekly_completed_email("desmond@crevalle.io", items) end) {:noreply, state} end def handle_info(:send_email, state) do items = Lily.WeeklySummary.this_week Lily.Mailer.send_weekly_completed_email("desmond@crevalle.io", items) {:noreply, state} end Task.async/1
22. Real Time
23. Real Time Phoenix • One process per client • holds state, does not take up CPU resources when doing nothing • Long-running request or file upload does not affect other users • System degrades gracefully, evenly under load
24. 2 Million Websocket Connections ! http://www.phoenixframework.org/blog/the-road-to-2-million-websocket-connections • 40-core CPU • 128GB RAM • Chat app with 2,000,000 users in single room • Publish message to all users with 1-2s latency • Hit Linux ulimit for available file descriptors
25. 2 Million Websocket Connections ! https://dockyard.com/blog/2016/08/09/phoenix-channels-vs-rails-action-cable ActionCable • 75 rooms, 3750 users • ~8.5s latency for message publish Contrast with ActionCable Phoenix • 1100 rooms, 55,000 users • ~0.5s latency for message publish 8 cores, 16GB RAM
26. 2 Million Websocket Connections ! https://dockyard.com/blog/2016/08/09/phoenix-channels-vs-rails-action-cable ActionCable • 75 rooms, 3750 users • ~8.5s latency for message publish • Redis dependency • Stop the World GC Contrast with ActionCable Phoenix • 1100 rooms, 55,000 users • ~0.5s latency for message publish 8 cores, 16GB RAM
27. Websocket the Planet! 7,000,000,000 humans ÷ 2,000,000 connections/server ========================== 3,500 servers
28. Everyone? probably won’t have 7,000,000,000 people trying to hail a taxicab in NYC at the same time it’s time to start thinking big.
29. users shouldn’t have to refresh the page realtime is free
30. thanks! Saturday, May 20 2017 http://empex.co