Make conn values and services path configurable at runtime

Connection values (such as redis server port and the port to run farside
on) as well as the services json file to use can now be set via
environment variables:

FARSIDE_PORT sets the port for Farside to run on
FARSIDE_REDIS_PORT sets the redis server port for Farside to use
FARSIDE_SERVICES_JSON sets the services json file for Farside to use

This partially addresses the move towards de-listing Cloudflare
instances by default by allowing different services json files to be
used with different redis servers.

See #43

README.md

@@ -108,3 +108,6 @@ request per second per IP.
 | Name | Purpose |
 | -- | -- |
 | FARSIDE_TEST | If enabled, bypasses the instance availability check and adds all instances to the pool. |
+| FARSIDE_PORT | The port to run Farside on (default: `4001`) |
+| FARSIDE_REDIS_PORT | The Redis server port to use (default: `6379`, same as the default for Redis) |
+| FARSIDE_SERVICES_JSON | The "services" JSON file to use for selecting instances (default: `services.json`) |

config/config.exs

@@ -1,13 +1,10 @@
 import Config
 
 config :farside,
-  port: 4001,
-  redis_conn: "redis://localhost:6379",
   update_file: ".update-results",
   service_prefix: "service-",
   fallback_suffix: "-fallback",
   previous_suffix: "-previous",
-  services_json: "services.json",
   index: "index.eex",
   route: "route.eex",
   headers: [

config/runtime.exs

@@ -0,0 +1,6 @@
+import Config
+
+config :farside,
+  port: System.get_env("FARSIDE_PORT", "4001"),
+  redis_conn: "redis://localhost:#{System.get_env("FARSIDE_REDIS_PORT", "6379")}",
+  services_json: System.get_env("FARSIDE_SERVICES_JSON", "services.json")

lib/farside/application.ex

@@ -1,22 +1,27 @@
 defmodule Farside.Application do
-  @farside_port Application.fetch_env!(:farside, :port)
-  @redis_conn Application.fetch_env!(:farside, :redis_conn)
+  #@farside_port Application.fetch_env!(:farside, :port)
+  #@redis_conn Application.fetch_env!(:farside, :redis_conn)
   @moduledoc false
 
   use Application
 
   @impl true
   def start(_type, _args) do
+    redis_conn = Application.fetch_env!(:farside, :redis_conn)
+    farside_port = Application.fetch_env!(:farside, :port)
+    IO.puts "Runing on http://localhost:#{farside_port}"
+    IO.puts "Redis conn: #{redis_conn}"
+
     children = [
       Plug.Cowboy.child_spec(
         scheme: :http,
         plug: Farside.Router,
         options: [
-          port: @farside_port
+          port: String.to_integer(farside_port)
         ]
       ),
       {PlugAttack.Storage.Ets, name: Farside.Throttle.Storage, clean_period: 60_000},
-      {Redix, {@redis_conn, [name: :redix]}},
+      {Redix, {redis_conn, [name: :redix]}},
       Farside.Scheduler,
       Farside.Server
     ]

lib/farside/instances.ex

@@ -1,7 +1,6 @@
 defmodule Farside.Instances do
   @fallback_suffix Application.fetch_env!(:farside, :fallback_suffix)
   @update_file Application.fetch_env!(:farside, :update_file)
-  @services_json Application.fetch_env!(:farside, :services_json)
   @service_prefix Application.fetch_env!(:farside, :service_prefix)
   @headers Application.fetch_env!(:farside, :headers)
   @queries Application.fetch_env!(:farside, :queries)
@@ -42,7 +41,8 @@ defmodule Farside.Instances do
   end
 
   def update() do
-    {:ok, file} = File.read(@services_json)
+    services_json = Application.fetch_env!(:farside, :services_json)
+    {:ok, file} = File.read(services_json)
     {:ok, json} = Jason.decode(file)
 
     # Loop through all instances and check each for availability

test/farside_test.exs

@@ -1,5 +1,4 @@
 defmodule FarsideTest do
-  @services_json Application.fetch_env!(:farside, :services_json)
 
   use ExUnit.Case
   use Plug.Test
@@ -49,7 +48,8 @@ defmodule FarsideTest do
   end
 
   test "/:service" do
-    {:ok, file} = File.read(@services_json)
+    services_json = Application.fetch_env!(:farside, :services_json)
+    {:ok, file} = File.read(services_json)
     {:ok, service_list} = Jason.decode(file)
 
     service_names =