simple cluster

Author: bigardone

simple_cluster/.formatter.exs

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+# Used by "mix format"
+[
+  inputs: ["{mix,.formatter}.exs", "{config,lib,test}/**/*.{ex,exs}"]
+]

simple_cluster/.gitignore

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+# The directory Mix will write compiled artifacts to.
+/_build/
+
+# If you run "mix test --cover", coverage assets end up here.
+/cover/
+
+# The directory Mix downloads your dependencies sources to.
+/deps/
+
+# Where third-party dependencies like ExDoc output generated docs.
+/doc/
+
+# Ignore .fetch files in case you like to edit your project deps locally.
+/.fetch
+
+# If the VM crashes, it generates a dump, let's ignore it too.
+erl_crash.dump
+
+# Also ignore archive artifacts (built via "mix archive.build").
+*.ez
+
+# Ignore package tarball (built via "mix hex.build").
+simple_cluster-*.tar
+
+
+# Temporary files for e.g. tests
+/tmp

simple_cluster/README.md

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+# SimpleCluster
+
+**TODO: Add description**
+
+## Installation
+
+If [available in Hex](https://hex.pm/docs/publish), the package can be installed
+by adding `simple_cluster` to your list of dependencies in `mix.exs`:
+
+```elixir
+def deps do
+  [
+    {:simple_cluster, "~> 0.1.0"}
+  ]
+end
+```
+
+Documentation can be generated with [ExDoc](https://github.com/elixir-lang/ex_doc)
+and published on [HexDocs](https://hexdocs.pm). Once published, the docs can
+be found at [https://hexdocs.pm/simple_cluster](https://hexdocs.pm/simple_cluster).
+

simple_cluster/lib/simple_cluster.ex

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+defmodule SimpleCluster do
+  defdelegate ping, to: SimpleCluster.Ping
+end

simple_cluster/lib/simple_cluster/application.ex

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+defmodule SimpleCluster.Application do
+  # See https://hexdocs.pm/elixir/Application.html
+  # for more information on OTP Applications
+  @moduledoc false
+
+  use Application
+
+  @impl true
+  def start(_type, _args) do
+    children = [
+      SimpleCluster.Observer,
+      SimpleCluster.Ping
+    ]
+
+    # See https://hexdocs.pm/elixir/Supervisor.html
+    # for other strategies and supported options
+    opts = [strategy: :one_for_one, name: SimpleCluster.Supervisor]
+    Supervisor.start_link(children, opts)
+  end
+end

simple_cluster/lib/simple_cluster/observer.ex

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+defmodule SimpleCluster.Observer do
+  @moduledoc """
+  Simple process that monitors node changes in the
+  current cluster.
+  """
+
+  use GenServer
+
+  require Logger
+
+  def start_link(_), do: GenServer.start_link(__MODULE__, Map.new())
+
+  @impl GenServer
+  def init(state) do
+    :net_kernel.monitor_nodes(true)
+
+    {:ok, state}
+  end
+
+  @impl GenServer
+  def handle_info({:nodedown, node}, state) do
+    # A node left the cluster
+    Logger.info("--- Node down: #{node}")
+
+    {:noreply, state}
+  end
+
+  def handle_info({:nodeup, node}, state) do
+    # A new node joined the cluster
+    Logger.info("--- Node up: #{node}")
+
+    {:noreply, state}
+  end
+end

simple_cluster/lib/simple_cluster/ping.ex

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+defmodule SimpleCluster.Ping do
+  @moduledoc """
+  Process which listens to `:ping` messages from other
+  nodes and responds with `:pong`.
+  """
+
+  use GenServer
+  require Logger
+
+  def start_link(_) do
+    GenServer.start_link(__MODULE__, Map.new(), name: __MODULE__)
+  end
+
+  @doc """
+  Takes all the existing nodes in the cluster and sends
+  a `:ping` message to them, logging the result.
+  """
+  def ping do
+    Node.list()
+    |> Enum.map(&GenServer.call({__MODULE__, &1}, :ping))
+    |> Logger.info()
+  end
+
+  @impl GenServer
+  def init(state), do: {:ok, state}
+
+  @impl GenServer
+  def handle_call(:ping, from, state) do
+    Logger.info("--- Receiving ping from #{inspect(from)}")
+
+    {:reply, {:ok, node(), :pong}, state}
+  end
+end

simple_cluster/mix.exs

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+defmodule SimpleCluster.MixProject do
+  use Mix.Project
+
+  def project do
+    [
+      app: :simple_cluster,
+      version: "0.1.0",
+      elixir: "~> 1.11",
+      start_permanent: Mix.env() == :prod,
+      deps: deps()
+    ]
+  end
+
+  # Run "mix help compile.app" to learn about applications.
+  def application do
+    [
+      extra_applications: [:logger],
+      mod: {SimpleCluster.Application, []}
+    ]
+  end
+
+  # Run "mix help deps" to learn about dependencies.
+  defp deps do
+    [
+      # {:dep_from_hexpm, "~> 0.3.0"},
+      # {:dep_from_git, git: "https://github.com/elixir-lang/my_dep.git", tag: "0.1.0"}
+    ]
+  end
+end

simple_cluster/sys.config

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+[{kernel,
+  [
+    {sync_nodes_optional, ['n1@127.0.0.1', 'n2@127.0.0.1']},
+    {sync_nodes_timeout, 5000}
+  ]}
+].

simple_cluster/test/simple_cluster_test.exs

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+defmodule SimpleClusterTest do
+  use ExUnit.Case
+  doctest SimpleCluster
+
+  test "greets the world" do
+    assert SimpleCluster.hello() == :world
+  end
+end

simple_cluster/test/test_helper.exs

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+ExUnit.start()