Exploring Elixir E7: Automatic Clustering

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Thanks for replying!

Running on:
MacOS Sierra 10.12.6
erlang/OTP 20
elixir 1.5.2
libcluster 2.2.3

Just cloned the repo and installed deps (nothing changed) and after successfully starting the first node with iex --sname node-1 -S mix and ExploringElixir.AutoCluster.start(), if i run lsof -i :45892 this shows up:

COMMAND      PID      USER   FD   TYPE   DEVICE    SIZE/OFF   NODE NAME
beam.smp     12427     me    35u  IPv4   0x1879...    0t0     UDP *:45892

Trying to start the second node iex --sname node-2 -S mix and ExploringElixir.AutoCluster.start() shows the error I previously mentioned:

** (Mix) Could not start application libcluster: Cluster.App.start(:normal, []) returned an error: shutdown: failed to start child: Cluster.Strategy.Gossip
** (EXIT) an exception was raised:
    ** (MatchError) no match of right hand side value: {:error, :eaddrinuse}
        (libcluster) lib/strategy/gossip.ex:56: Cluster.Strategy.Gossip.init/1
        (stdlib) gen_server.erl:365: :gen_server.init_it/2
        (stdlib) gen_server.erl:333: :gen_server.init_it/6
        (stdlib) proc_lib.erl:247: :proc_lib.init_p_do_apply/3

Changing the port: <some_other_number> didn’t fix the issue, I even tried to set the port to 0 so a random and available one is picked, in this way the second node can successfully start but it wont be able to automatically connect to the first or any other node.

This is my config/libcluster.exs:

config :libcluster,
  topologies: [
    exploring_elixir: [
      strategy: Cluster.Strategy.Gossip,
      config: [
        port: 45892 # tried other ports, not solving it    
      ]
      # everything else...
    ]
  ]

Maybe I’m just not getting the

if_addr: {0,0,0,0},
multicast_addr: {230,1,1,251}

configuration part, or some other setup is required to run multiple nodes in dev mode.

As far as I know a UDP socket can’t share the same address/port with other process or be restarted:

iex(1)> :gen_udp.open(8789)
{:ok, #Port<0.1174>}
# on the same or another shell ->
iex(2)> :gen_udp.open(8789)
{:error, :eaddrinuse}

but in your screencast it seems to work fine, so I’m confused haha.

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