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defmodule Yourapp.YourWorker do
  use GenServer

  def start_link(state) do
    GenServer.start_link(__MODULE__, state)
  end

  def init(opts) do
    initial_state = initialize_worker(opts)

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  # Change the handling of :begin_handoff
  # This is triggered whenever a registered process is to be killed.
  def handle_call({:swarm, :begin_handoff}, _from, current_state) do
    {:reply, {:resume, produce_outgoing_state(current_state)}, current_state}
  end

  # Handle :end_handoff
  # This is triggered whenever a process has been restarted on a new node.
  def handle_call({:swarm, :end_handoff, incoming_state}, _from, current_state) do
    {:noreply, end_handoff_new_state(current_state, incoming_state)}

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defmodule Yourapp.YourSupervisor do
  use DynamicSupervisor

  # See https://hexdocs.pm/elixir/Application.html
  # for more information on OTP Applications
  def start_link(state) do
    DynamicSupervisor.start_link(__MODULE__, state, name: __MODULE__)
  end

  def init(_) do

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### In config/config.exs
config :libcluster,
  topologies: [
    your_app: [
      strategy: Cluster.Strategy.Gossip,
      config: [
        port: 45892,
        if_addr: "0.0.0.0",
        multicast_addr: "230.1.1.251",
        multicast_ttl: 1

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# In Dockerfile:
ENTRYPOINT ["/opt/app/docker-entrypoint-dev.sh"]

# In docker-entrypoint-dev.sh:
if [ -z ${NODE_IP+x} ]; then
    export NODE_IP="$(hostname -i | cut -f1 -d' ')"
fi

elixir --name yourapp@${NODE_IP} --cookie "your_dev_erlang_cookie" -S mix phx.server

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### In mix.exs
  defp deps do
    [
      ...
      {:libcluster, "~> 3.1"},
      ...
    ]
  end

### In config/prod.exs

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Swarm.register_name(
  :unique_name_for_this_worker_process,
  Yourapp.YourSupervisor,
  :register,
  [Yourapp.YourWorker]
)

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services:
  your_app: &app
    build:
      context: ./app
    ports:
      - 4000:4000
    # ...

  your_app_2:
    <<: *app

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### In config/config.exs
config :libcluster,
  topologies: [
    your_app: [
      strategy: Cluster.Strategy.Gossip,
      config: [
        port: 45892,
        if_addr: "0.0.0.0",
        multicast_addr: "230.1.1.251",
        multicast_ttl: 1

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### In mix.exs
  defp deps do
    [
      ...
      {:libcluster, "~> 3.1"},
      ...
    ]
  end

### In config/prod.exs