Node Whitelisting doesn't prevent the unexpected nodes into Swarm's clustering

[xinz]

Hi,

I'm new to Swarm, I find the following case doesn't work as expected, please advise if any misunderstanding.

1, Here is node whitelist config in config.exs:

config :swarm,
  debug: true,
  node_whitelist: [~r/^app[\d]@.*$/]

2, Here is libcluster config in dev.exs:

config :libcluster,
  topologies: [
    main: [
    strategy: Cluster.Strategy.Epmd,
    config: [hosts: [:"app1@server"]],
    connect: {:net_kernel, :connect, []},
  ]
]

3, I run the following commands to setup nodes in order
$iex --sname app1 -S mix
$iex --sname unknown -S mix

4, Refer the Example in https://hexdocs.pm/swarm/readme.html , I start some workers in unknown node, and then I find some workers started in app1 node as expected, but some workers started in unknown node as unexpected, why the Swarm's distribution algorithm will use the excluded nodes (NOT in node whitelist) to register workers?

Hex env:
Hex: 0.15.0
Elixir: 1.4.2
OTP: 19.2.3

Deps tree:
├── libcluster ~> 2.0 (Hex package)
│ └── poison ~> 3.0 (Hex package)
├── timex ~> 3.0 (Hex package)
│ ├── combine ~> 0.7 (Hex package)
│ ├── gettext ~> 0.10 (Hex package)
│ └── tzdata ~> 0.1.8 or ~> 0.5 (Hex package)
│ └── hackney ~> 1.0 (Hex package)
│ ├── certifi 1.0.0 (Hex package)
│ ├── idna 4.0.0 (Hex package)
│ ├── metrics 1.0.1 (Hex package)
│ ├── mimerl 1.0.2 (Hex package)
│ └── ssl_verify_fun 1.1.1 (Hex package)
├── sweet_xml ~> 0.6.5 (Hex package)
├── httpoison ~> 0.11.0 (Hex package)
│ └── hackney ~> 1.7.0 (Hex package)
├── swarm ~> 3.0 (Hex package)
│ ├── gen_state_machine ~> 2.0 (Hex package)
│ └── libring ~> 1.0 (Hex package)
└── distillery ~> 1.0 (Hex package)

Thanks

[xinz]

Here's a PR for this fix, hope it makes sense #32

[xinz]

Currently, clone the latest code from master branch, I occurred this issue

13:36:06.259 [error] GenStateMachine Swarm.Tracker terminating
** (ErlangError) erlang error: {:"module could not be loaded", Swarm.Distribution.Strategy.Ring}
    (swarm) lib/swarm/distribution/strategy.ex:40: Swarm.Distribution.Strategy.create/1
    (swarm) lib/swarm/tracker/tracker.ex:124: Swarm.Tracker.init/1
    (stdlib) gen_statem.erl:626: :gen_statem.init_it/6
    (stdlib) proc_lib.erl:247: :proc_lib.init_p_do_apply/3
State: :undefined
Callback mode: :undefined

I modify this line in distribution/strategy.ex to resolve it, or rename module name "Swarm.Distribution.Ring" in distribution/ring.ex.

-alias Swarm.Distribution.Strategy.Ring, as: RingStrategy
+alias Swarm.Distribution.Ring, as: RingStrategy