Knee-Deep Into P2P: A Tale of Fail (non-Elixir)

The slides for my talk at Lambda Days 2018 (www.lambdadays.org/lambdadays2018)

Transcript

1. Knee-Deep Into P2P A Tale of Fail @fribmendes
2. Knee-Deep Into P2P A Tale of Fail @fribmendes
3. “This is SOOO boring…” - me, circa last year or smth
7. “This is SOOO boring…” - me, 10 months ago
13. “ ” - me, whenever I get to play with distributed systems
15. I don’t know how to smart office
16. I know how to web development
17. I know how to web development … what now?
19. Step 1: receive new connections
20. Step 1: receive new connections Step 2: accept and send messages
21. Step 1: receive new connections Step 2: accept and send messages Step 3: do a bunch of Steps 1 and 2
22. Step 1: receive new connections
24. defmodule Gossip.Server do def listen(pid, port) do {:ok, server_socket} = :gen_tcp.listen(port, @socket_opts) accept_loop(pid, server_socket) end defp accept_loop(pid, server_socket) do {:ok, client} = :gen_tcp.accept(server_socket) :inet.setopts(client, [active: true]) :gen_tcp.controlling_process(client, pid) Gossip.accept(pid, client) accept_loop(pid, server_socket) end end
25. defmodule Gossip.Server do def listen(pid, port) do {:ok, server_socket} = :gen_tcp.listen(port, @socket_opts) accept_loop(pid, server_socket) end defp accept_loop(pid, server_socket) do {:ok, client} = :gen_tcp.accept(server_socket) :inet.setopts(client, [active: true]) :gen_tcp.controlling_process(client, pid) Gossip.accept(pid, client) accept_loop(pid, server_socket) end end
26. Step 1: receive new connections Step 2: accept and send messages
28. defmodule Gossip.Worker do def recv_loop(pid, socket) do continue = receive do {:tcp, _port, msg} -> Gossip.recv(pid, msg) true {:tcp_closed, port} -> :gen_tcp.close(port) Gossip.disconnect(pid, self()) false {:send, msg} -> :gen_tcp.send(socket, msg) true end continue and recv_loop(pid, socket) end end
29. defmodule Gossip.Worker do def recv_loop(pid, socket) do continue = receive do {:tcp, _port, msg} -> Gossip.recv(pid, msg) true {:tcp_closed, port} -> :gen_tcp.close(port) Gossip.disconnect(pid, self()) false {:send, msg} -> :gen_tcp.send(socket, msg) true end continue and recv_loop(pid, socket) end end
30. Step 1: receive new connections Step 2: accept and send messages Step 3: do a bunch of Steps 1 and 2
31. Raspberry Pi #1 Raspberry Pi #2
34. “Does it scale?”
36. Time to copy off the internet find a creative solution
38. g
39. Gnutella
40. Gnutella
41. Gnutella
42. Gnutella
43. Gnutella
44. g (gnutella2)
45. Gnutella
46. G2/Gnutella2
47. G2/Gnutella2
48. G2/Gnutella2
49. G2/Gnutella2
55. HyParView
62. Plumtrees
63. Optimal number of messages
64. But you can’t afford to lose nodes
75. “Aha! It works on my computer!”
76. “Great but we need something to show”
77. “Great but we need something to show” (aka Raspberry Pi time)
78. “Sure. Seems legit…” — @iampfac
79. “Wait. He works here!?” — @naps62
80. “Hey, I can borrow™ someone else’s code”
84. you shall not pass!
85. Solution: stick everything on Raspberry Pi’s
86. Things running on one Raspberry Pi
87. Things running on one Raspberry Pi ✓BEAM
88. Things running on one Raspberry Pi ✓BEAM ✓thebox (sensors)
89. Things running on one Raspberry Pi ✓BEAM ✓thebox (sensors) ✓Phoenix app
90. Things running on one Raspberry Pi ✓BEAM (x2) ✓thebox (sensors) ✓Phoenix app
91. Things running on one Raspberry Pi ✓BEAM (x2) ✓thebox (sensors) ✓Phoenix app ✓Postgres
92. Things running on one Raspberry Pi ✓BEAM (x2) ✓thebox (sensors) ✓Phoenix app ✓Postgres ✓Cassandra
93. Things running on one Raspberry Pi ✓BEAM (x2) ✓thebox (sensors) ✓Phoenix app ✓Postgres ✓Cassandra it works!
96. @antenna = Satellite::Antenna.new(host, port) @antenna.on(“data") do |data| if data.avg_temp > 25 slack.send_msg(“people, it's too hot") end end @antenna.on("lights") do |payload, data| payload == "on" ? turn_lights_on : turn_lights_off end @antenna.watch
97. “Looking good! Everything’s working!”
99. State of each node:
100. State of each node: • Last sensor readings
101. State of each node: • Last sensor readings • Network map (MAC-IP)
102. State of each node: • Last sensor readings • Network map (MAC-IP) • Target values
103. State of each node: • Last sensor readings • Network map (MAC-IP) • Target values
105. How do we handle concurrency?
108. No database locks. No transactions. You’re on your own, kiddo.
109. Vector Clocks
117. Shared state and why it sucks
118. Vector = (1, 0) Vector = (0, 1)
119. CAP Theorem
120. CAP Theorem “you’re a programmer. you can’t have nice things.”
121. consistency availability partitioning
122. consistency availability partitioning
123. Eventual Consistency
124. CRDTs
125. Operation-Based CRDT
126. Operation-Based CRDT commutative but not idempotent update exactly once
127. no CRDTs
128. no CRDTs
129. no CRDTs
130. no CRDTs
131. Op-based CRDTs
132. Op-based CRDTs
133. Op-based CRDTs
134. Op-based CRDTs
135. State-Based CRDT
136. State-Based CRDT commutative and idempotent heavier on the network
137. State-based CRDTs
138. State-based CRDTs
139. State-based CRDTs
140. State-based CRDTs
148. Wrapping up
149. System resources matter
150. System resources matter your algorithms should account for them
151. There are models. Use them.
152. Distributed System Checklist
153. Distributed System Checklist •Is the number of processes known or finite?
154. Distributed System Checklist •Is the number of processes known or finite? •Is there a global notion of time?
155. Distributed System Checklist •Is the number of processes known or finite? •Is there a global notion of time? •Is the network reliable?
156. Distributed System Checklist •Is the number of processes known or finite? •Is there a global notion of time? •Is the network reliable? •Is there full connectivity?
157. Distributed System Checklist •Is the number of processes known or finite? •Is there a global notion of time? •Is the network reliable? •Is there full connectivity? •What happens when a process crashes?
158. It really doesn’t change that much
159. CRDTs aren’t a golden hammer
160. Reinventing the wheel is stupid
162. Knee-Deep Into P2P A Tale of Fail @fribmendes