Erlang

Setup a cluster on a LAN

• Make sure UDP / TCP port 4369 is open

erl -name muh -setcookie somesecret
erl -name maeh -setcookie somesecret

Setup a cluster over SSH

• On master node (make sure your user can connect to the slaves by passwordless ssh key e.g. ssh-copy-id)

erl -rsh ssh -sname master

• Compile and load cluster module on master

-module(cluster).
-export([slaves/1]).

slaves([]) -> ok;
slaves([Host|Hosts]) ->
    {ok, Node} = slave:start_link(Host, "slave", "-rsh ssh"),
    io:format("Erlang node started = [~p]~n", [Node]),
    slaves(Hosts).

• Start the cluster from master node

erl> cluster:slaves(["node1", "node2", "node3"]).

List all processes

i().
regs().

List all connected nodes

nodes().

Spawn process on remote node

rpc:spawn(Node, Mod, Fun, Args).

Call function on remote node

rpc:call(Node, Pid, Fun, Args).

Call a function on all connected nodes

rpc:multicall(nodes(), Mod, Fun, Args).

Concurrent program template

-module(ctemplate).
-compile(export_all).

start() -> spawn(ctemplate, loop, []).

rpc(Pid, Request) ->
    Pid ! {self(), Request},
    receive
        {Pid, Response} -> Response.
    end.

loop() ->
    receive
        Any ->
            io:format("Help me do something"),
            loop()
     end.