feat: configure dnscluster to allow multi-node

* Configure `docker-compose` to scale at least 2 nodes.
* Add script to start service with proper naming
* Create custom resolver.
  * This is not strictly necessary.

config/dev.exs

@@ -1,5 +1,9 @@
 import Config
 
+config :wabanex,
+  dns_cluster_query: :ignore,
+  dns_cluster_resolver: Wabanex.DevDNSClusterResolver
+
 # Configure your database
 config :wabanex, Wabanex.Repo,
   database: "wabanex_dev",

config/runtime.exs

@@ -1,5 +1,7 @@
 import Config
 
+config :wabanex, dns_cluster_query: System.get_env("DNS_CLUSTER_QUERY") || :ignore
+
 config :wabanex, Wabanex.Repo,
   username: System.get_env("POSTGRES_USER") || "postgres",
   password: System.get_env("POSTGRES_PASS") || "postgres",

docker-compose.yml

@@ -43,12 +43,14 @@ services:
         - path: ./mix.lock
           action: rebuild
     environment: &app_environment
+      DNS_CLUSTER_QUERY: *app_host
       POSTGRES_HOST: *db_host
       POSTGRES_USER: *db_user
       POSTGRES_PASS: *db_pass
       POSTGRES_NAME: wabanex_dev
     working_dir: /opt/app
     restart: unless-stopped
+    scale: 2
     entrypoint: sleep
     command: infinity
   db_setup:

lib/wabanex/application.ex

@@ -15,6 +15,10 @@ defmodule Wabanex.Application do
       WabanexWeb.Telemetry,
       # Start the PubSub system
       {Phoenix.PubSub, name: Wabanex.PubSub},
+      {DNSCluster,
+       query: Application.get_env(:wabanex, :dns_cluster_query) || :ignore,
+       log: :info,
+       resolver: Application.get_env(:wabanex, :dns_cluster_resolver) || DNSCluster.Resolver},
       # Start the Endpoint (http/https)
       WabanexWeb.Endpoint
       # Start a worker by calling: Wabanex.Worker.start_link(arg)

lib/wabanex/dev_dns_cluster_resolver.ex

@@ -0,0 +1,26 @@
+defmodule Wabanex.DevDNSClusterResolver do
+  @moduledoc """
+  Local DNS resolver for cluster query.
+  """
+  require Record
+
+  Record.defrecord(:hostent, Record.extract(:hostent, from_lib: "kernel/include/inet.hrl"))
+
+  def basename(node_name) when is_atom(node_name) do
+    [basename, _] = node_name |> to_string() |> String.split("@")
+    basename
+  end
+
+  def connect_node(node_name) when is_atom(node_name) do
+    Node.connect(node_name)
+  end
+
+  def list_nodes, do: Node.list(:visible)
+
+  def lookup(query, type) when is_binary(query) and type in [:a, :aaaa] do
+    case :inet_res.getbyname(~c"#{query}", type) do
+      {:ok, hostent(h_addr_list: addr_list)} -> addr_list
+      {:error, _} -> []
+    end
+  end
+end

mix.exs

@@ -36,6 +36,7 @@ defmodule Wabanex.MixProject do
       {:credo, "~> 1.7.0", only: [:dev, :test], runtime: false},
       {:crudry, "~> 2.4.0"},
       {:dialyxir, "~> 1.4.0", only: [:dev, :test], runtime: false},
+      {:dns_cluster, "~> 0.1.1"},
       {:ecto_sql, "~> 3.12.0"},
       {:gettext, "~> 0.25.0"},
       {:jason, "~> 1.4.0"},

mix.lock

@@ -11,6 +11,7 @@
   "db_connection": {:hex, :db_connection, "2.7.0", "b99faa9291bb09892c7da373bb82cba59aefa9b36300f6145c5f201c7adf48ec", [:mix], [{:telemetry, "~> 0.4 or ~> 1.0", [hex: :telemetry, repo: "hexpm", optional: false]}], "hexpm", "dcf08f31b2701f857dfc787fbad78223d61a32204f217f15e881dd93e4bdd3ff"},
   "decimal": {:hex, :decimal, "2.1.1", "5611dca5d4b2c3dd497dec8f68751f1f1a54755e8ed2a966c2633cf885973ad6", [:mix], [], "hexpm", "53cfe5f497ed0e7771ae1a475575603d77425099ba5faef9394932b35020ffcc"},
   "dialyxir": {:hex, :dialyxir, "1.4.3", "edd0124f358f0b9e95bfe53a9fcf806d615d8f838e2202a9f430d59566b6b53b", [:mix], [{:erlex, ">= 0.2.6", [hex: :erlex, repo: "hexpm", optional: false]}], "hexpm", "bf2cfb75cd5c5006bec30141b131663299c661a864ec7fbbc72dfa557487a986"},
+  "dns_cluster": {:hex, :dns_cluster, "0.1.3", "0bc20a2c88ed6cc494f2964075c359f8c2d00e1bf25518a6a6c7fd277c9b0c66", [:mix], [], "hexpm", "46cb7c4a1b3e52c7ad4cbe33ca5079fbde4840dedeafca2baf77996c2da1bc33"},
   "ecto": {:hex, :ecto, "3.12.0", "9014a3ccac7f91e680b9d237d461ebe3d4e16d62ca8e355d540e2c6afdc28309", [:mix], [{:decimal, "~> 2.0", [hex: :decimal, repo: "hexpm", optional: false]}, {:jason, "~> 1.0", [hex: :jason, repo: "hexpm", optional: true]}, {:telemetry, "~> 0.4 or ~> 1.0", [hex: :telemetry, repo: "hexpm", optional: false]}], "hexpm", "41e781a76e131093af8e1edf68b1319bf320878faff58da41ffa4b10fc6ff678"},
   "ecto_sql": {:hex, :ecto_sql, "3.12.0", "73cea17edfa54bde76ee8561b30d29ea08f630959685006d9c6e7d1e59113b7d", [:mix], [{:db_connection, "~> 2.4.1 or ~> 2.5", [hex: :db_connection, repo: "hexpm", optional: false]}, {:ecto, "~> 3.12", [hex: :ecto, repo: "hexpm", optional: false]}, {:myxql, "~> 0.7", [hex: :myxql, repo: "hexpm", optional: true]}, {:postgrex, "~> 0.19 or ~> 1.0", [hex: :postgrex, repo: "hexpm", optional: true]}, {:tds, "~> 2.1.1 or ~> 2.2", [hex: :tds, repo: "hexpm", optional: true]}, {:telemetry, "~> 0.4.0 or ~> 1.0", [hex: :telemetry, repo: "hexpm", optional: false]}], "hexpm", "dc9e4d206f274f3947e96142a8fdc5f69a2a6a9abb4649ef5c882323b6d512f0"},
   "erlex": {:hex, :erlex, "0.2.7", "810e8725f96ab74d17aac676e748627a07bc87eb950d2b83acd29dc047a30595", [:mix], [], "hexpm", "3ed95f79d1a844c3f6bf0cea61e0d5612a42ce56da9c03f01df538685365efb0"},

priv/docker/service/docker-entrypoint.sh

@@ -0,0 +1,2 @@
+#!/usr/bin/env bash
+elixir --name ${HOSTNAME}@$(hostname -i | cut -d ' ' -f1) --cookie ${1} -S mix phx.server