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Knee-Deep Into P2P: A Tale of Fail (PWL Porto)
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Fernando Mendes
May 23, 2018
Programming
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Knee-Deep Into P2P: A Tale of Fail (PWL Porto)
Fernando Mendes
May 23, 2018
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Transcript
Knee-Deep Into P2P A Tale of Fail @fribmendes
Knee-Deep Into P2P A Tale of Fail @fribmendes
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I don’t know how to smart office
I don’t know how to smart office … what now?
@fribmendes me failing at photoshop
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I don’t know how to smart office … what now?
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Step 1: receive new connections
Step 1: receive new connections Step 2: accept and send
messages
Step 1: receive new connections Step 2: accept and send
messages Step 3: do a bunch of Steps 1 and 2
Step 1: receive new connections
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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
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
Step 1: receive new connections Step 2: accept and send
messages
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def recv_loop(pid, socket) do receive do {:tcp, _port, msg} ->
# process an incoming message {:tcp_closed, port} -> # close the sockets {:send, msg} -> # send an outgoing message end end end
Step 1: receive new connections Step 2: accept and send
messages Step 3: do a bunch of Steps 1 and 2
Raspberry Pi #1 Raspberry Pi #2
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“Does it scale?”
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g
Gnutella
Gnutella
Gnutella
Gnutella
Gnutella
g
g (gnutella2)
Gnutella
G2/Gnutella2
G2/Gnutella2
G2/Gnutella2
G2/Gnutella2
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HyParView
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Plumtrees
Optimal number of messages
But you can’t afford to lose nodes
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“Aha! It works on my computer!”
“Aha! It works on my computer!”
“Great but we need something to show”
“Great but we need something to show” (aka Raspberry Pi
time)
“Guys… Is this a bomb? Are we going to die?”
— @naps62
“Hey, I can borrow™ someone else’s code”
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you shall not pass!
Stick everything on Raspberry Pi’s
Things running on one Raspberry Pi
Things running on one Raspberry Pi ✓BEAM
Things running on one Raspberry Pi ✓BEAM ✓thebox (sensors)
Things running on one Raspberry Pi ✓BEAM ✓thebox (sensors) ✓Phoenix
app
Things running on one Raspberry Pi ✓BEAM (x2) ✓thebox (sensors)
✓Phoenix app
Things running on one Raspberry Pi ✓BEAM (x2) ✓thebox (sensors)
✓Phoenix app ✓Postgres
Things running on one Raspberry Pi ✓BEAM (x2) ✓thebox (sensors)
✓Phoenix app ✓Postgres ✓Cassandra
Things running on one Raspberry Pi ✓BEAM (x2) ✓thebox (sensors)
✓Phoenix app ✓Postgres ✓Cassandra it works!
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“Looking good! Everything’s working!”
lol, nope
State of each node:
State of each node: • Last sensor readings
State of each node: • Last sensor readings • Network
map (MAC-IP)
State of each node: • Last sensor readings • Network
map (MAC-IP) • Target values
State of each node: • Last sensor readings • Network
map (MAC-IP) • Target values
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How do we handle concurrency?
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No database locks. No transactions. You’re on your own, kiddo.
Vector Clocks
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Vector = (1, 0) Vector = (0, 1)
CAP Theorem
CAP Theorem “you’re a programmer. you can’t have nice things.”
consistency availability partitioning
consistency availability partitioning
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Eventual Consistency
CRDTs
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Operation-Based CRDT
Operation-Based CRDT commutative but not idempotent update exactly once
no CRDTs
no CRDTs
no CRDTs
no CRDTs
Op-based CRDTs
Op-based CRDTs
Op-based CRDTs
Op-based CRDTs
State-Based CRDT
State-Based CRDT commutative and idempotent heavier on the network
State-based CRDTs
State-based CRDTs
State-based CRDTs
State-based CRDTs
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Wrapping up
System resources matter
System resources matter your algorithms should account for them
There are models. Use them.
Distributed System Checklist
Distributed System Checklist •Is the number of processes known or
finite?
Distributed System Checklist •Is the number of processes known or
finite? •Is there a global notion of time?
Distributed System Checklist •Is the number of processes known or
finite? •Is there a global notion of time? •Is the network reliable?
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?
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?
It really doesn’t change that much
CRDTs aren’t a golden hammer
Reinventing the wheel is stupid
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Knee-Deep Into P2P A Tale of Fail @fribmendes