Introduction To Distributed Erlang

Introduction to Distributed Erlang Basic principles and a little more

About us Developing a new breed of platform for social networking games Scalability is a must Back-end developed with Erlang/OTP And lots of other good stuff Front-end developed with Flex 4

About me More stickers than a 40 years old RV!

Agenda and non-agenda Quick recap of message passing Core principles of Erlang remoting Global registry and process groups Nothing on Erlang syntax {<<"sorry">>} Nothing on custom networking nor OTP OTP is what you'll use in reality

Why Erlang for concurrency? Immutability painted all over it Designed to handle thousands of processes Spawned (not started nor forked) Processes communicate asynchronously Passing messages by value

Message sending As easy as: Pid ! Message Sends a message to a process inbox Like with mail delivery: Not sure if the letter reached its destination Needs a letter back if a response is needed

RSVP Add address on the envelope for a response

RSVP (client) Client is also Server's public API send(Sid, Message) -> Sid!{self(), Message}, receive {From, Response} -> io:format("Client ~p from ~p~n", [Response, From]) after 1000 -> bail end.

RSVP (server) start() -> spawn(fun()-> serve() end). serve() -> receive {From, Message} -> io:format("Server ~p from ~p~n", [Message, From]), From!{self(), {ack, Message}}, serve() end.

Process registration Allows process naming: register(my_pid, Pid). Frees application from passing Pids around: my_pid ! Message.

RPC strikes back Call MFA on single or multiple nodes Declined in zillions of variations: Blocking or not Parallelized, including pmap Makes code location aware Heterogeneous styles: Pid ! Message rpc:call(N,M,F,A)

Node connectivity Triggered by: rpc:call ... net_adm:ping(node@host) Nodes shake hands and share information Processes, registrations... Transitive mechanism Node 1 ➟ Node 2 and Node 2 ➟ Node3 then: Node 1 ➟ Node 3

Erlang Port Mapper Daemon

Erlang's magic cookie Passed on startup: erl -sname n1 -setcookie=secret Proper node and host naming required Coarse grained security Party time or bust!

Global process registry Location transparency: global:register_name(gbs, Sid). global:whereis_name(gbs) ! Message. Wired-in name conflict resolution Still need to ping nodes

Process group (1/3) Distributed named process group Processes join and leave: pg2:create(mypg2). pg2:join(mypg2, Sid). pg2:leave(mypg2, Sid).

Process group (2/3) pg2 can be used to send messages to: all processes: pg2:get_members(mypg2) local processes: pg2:get_local_members(mypg2) closest / random process: pg2:get_closest_pid(mypg2)

Process group (3/3) Also: pg (experimental)

Ping pong pang relief net_adm:world and net_adm:world_list Ease node discovery on hosts Requires hosts list Node discovery with nodefinder UDP multicast S3 list for AWS

Probing further

Thank you!

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Introduction To Distributed Erlang

by David Dossot on Jan 07, 2010

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