Output available instances and fallback URL to redis

Once a list of available URLs has been determined for a particular
service, the list is written as "service -> [list of instances]" to a
local redis connection. These can then be used in the greater routing
logic to pick a random instance from the list, or use a fallback
instance if none are determined to be available.

instances.json

@@ -1,18 +0,0 @@
-[
-    {
-        "instance_type": "reddit",
-        "instance_test": "/r/popular",
-        "instance_list": [
-            "https://libredd.it",
-            "https://libreddit.spike.codes"
-        ]
-    },
-    {
-        "instance_type": "instagram",
-        "instance_test": "/taylorswift",
-        "instance_list": [
-            "https://bibliogram.art/u",
-            "https://bibliogram.snopyta.org/u"
-        ]
-    }
-]

mix.exs

@@ -25,7 +25,8 @@ defmodule RouterExample.MixProject do
       {:jason, "~> 1.1"},
       {:plug_cowboy, "~> 2.0"},
       {:poison, "~> 5.0"},
-      {:httpoison, "~> 1.8"}
+      {:httpoison, "~> 1.8"},
+      {:redix, "~> 1.1"}
     ]
   end
 end

mix.lock

@@ -16,6 +16,7 @@
   "plug_crypto": {:hex, :plug_crypto, "1.2.2", "05654514ac717ff3a1843204b424477d9e60c143406aa94daf2274fdd280794d", [:mix], [], "hexpm", "87631c7ad914a5a445f0a3809f99b079113ae4ed4b867348dd9eec288cecb6db"},
   "poison": {:hex, :poison, "5.0.0", "d2b54589ab4157bbb82ec2050757779bfed724463a544b6e20d79855a9e43b24", [:mix], [{:decimal, "~> 2.0", [hex: :decimal, repo: "hexpm", optional: true]}], "hexpm", "11dc6117c501b80c62a7594f941d043982a1bd05a1184280c0d9166eb4d8d3fc"},
   "ranch": {:hex, :ranch, "1.8.0", "8c7a100a139fd57f17327b6413e4167ac559fbc04ca7448e9be9057311597a1d", [:make, :rebar3], [], "hexpm", "49fbcfd3682fab1f5d109351b61257676da1a2fdbe295904176d5e521a2ddfe5"},
+  "redix": {:hex, :redix, "1.1.4", "d66fc83d2d4f136c838568d1ec8b0c1a72acfcecfac88a40f86f60aaee883c93", [:mix], [{:castore, "~> 0.1.0", [hex: :castore, repo: "hexpm", optional: true]}, {:telemetry, "~> 0.4.0 or ~> 1.0", [hex: :telemetry, repo: "hexpm", optional: false]}], "hexpm", "515eff055b7de8967e835f4de22a6cfe8311bc1b8fe72f48200238fb43f6a803"},
   "ssl_verify_fun": {:hex, :ssl_verify_fun, "1.1.6", "cf344f5692c82d2cd7554f5ec8fd961548d4fd09e7d22f5b62482e5aeaebd4b0", [:make, :mix, :rebar3], [], "hexpm", "bdb0d2471f453c88ff3908e7686f86f9be327d065cc1ec16fa4540197ea04680"},
   "telemetry": {:hex, :telemetry, "1.0.0", "0f453a102cdf13d506b7c0ab158324c337c41f1cc7548f0bc0e130bbf0ae9452", [:rebar3], [], "hexpm", "73bc09fa59b4a0284efb4624335583c528e07ec9ae76aca96ea0673850aec57a"},
   "unicode_util_compat": {:hex, :unicode_util_compat, "0.7.0", "bc84380c9ab48177092f43ac89e4dfa2c6d62b40b8bd132b1059ecc7232f9a78", [:rebar3], [], "hexpm", "25eee6d67df61960cf6a794239566599b09e17e668d3700247bc498638152521"},

services.json

@@ -0,0 +1,20 @@
+[
+    {
+        "type": "reddit",
+        "test_url": "/r/popular",
+        "fallback": "https://libredd.it",
+        "instances": [
+            "https://libredd.it",
+            "https://libreddit.spike.codes"
+        ]
+    },
+    {
+        "type": "instagram",
+        "test_url": "/taylorswift",
+        "fallback": "https://bibliogram.art/u",
+        "instances": [
+            "https://bibliogram.art/u",
+            "https://bibliogram.snopyta.org/u"
+        ]
+    }
+]

update.exs

@@ -1,8 +1,9 @@
-defmodule Instance do
+defmodule Service do
   defstruct [
-    instance_type: nil,
-    instance_test: nil,
-    instance_list: []
+    type: nil,
+    test_url: nil,
+    fallback: nil,
+    instances: []
   ]
 end
 
@@ -18,16 +19,52 @@ defmodule Instances do
   end
 
   def update(filename) do
+    {:ok, conn} = Redix.start_link(
+      "redis://localhost:6379",
+      name: :redix
+    )
     {:ok, file} = File.read(filename)
-    {:ok, json} = Poison.decode(file, as: [%Instance{}])
+    {:ok, json} = Poison.decode(file, as: [%Service{}])
+
+    # Loop through all instances and check each for availability
     for service <- json do
-      result = Enum.filter(service.instance_list, fn(url) ->
-        request(url <> service.instance_test) == :good
+      result = Enum.filter(service.instances, fn(instance_url) ->
+        request(instance_url <> service.test_url) == :good
       end)
-      # TODO: Output result to redis
-      IO.inspect(result)
+
+      add_to_redis(conn, service, result)
+    end
+  end
+
+  def add_to_redis(conn, service, instances) do
+    # Remove previous list of instances
+    Redix.command(conn, [
+      "DEL",
+      service.type
+    ])
+
+    # Update with new list of available instances
+    Redix.command(conn, [
+      "LPUSH",
+      service.type
+    ] ++ instances)
+
+    # Set fallback to one of the available instances,
+    # or the default instance if all are "down"
+    if Enum.count(instances) > 0 do
+      Redix.command(conn, [
+        "SET",
+        service.type <> "-fallback",
+        Enum.random(instances)
+      ])
+    else
+      Redix.command(conn, [
+        "SET",
+        service.type <> "-fallback",
+        service.fallback
+      ])
     end
   end
 end
 
-Instances.update("instances.json")
+Instances.update("services.json")