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 gamesScalability is a must Back-end developed with Erlang/OTP

And lots of other good stuffFront-end developed with Flex 4

About me

More stickers than a 40 years old RV!

Agenda and non-agenda

Quick recap of message passingCore principles of Erlang remotingGlobal registry and process groupsNothing 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 itDesigned to handle thousands of processes

Spawned (not started nor forked)Processes communicate asynchronouslyPassing messages by value

Message sending

As easy as:

Pid ! MessageSends a message to a process inboxLike with mail delivery:

Not sure if the letter reached its destinationNeeds a letter back if a response is needed

RSVP

Add address on the envelope for a response

RSVP (client)

send(Sid, Message) -> Sid!{self(), Message}, receive {From, Response} -> io:format("Client ~p from ~p~n", [Response, From]) after 1000 -> bail end.

Client is also Server's public

API

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 nodesDeclined in zillions of variations:

Blocking or notParallelized, including pmap

Makes code location awareHeterogeneous 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 ➟ Node3then: Node 1 ➟ Node 3

Erlang Port Mapper Daemon

Erlang's magic cookie

Passed on startup:

erl -sname n1 -setcookie=secretProper node and host naming requiredCoarse 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 resolutionStill 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_listEase node discovery on hostsRequires hosts list

Node discovery with nodefinderUDP multicast S3 list for AWS

Probing further

Thank you!