Display list of available instances on home page

This introduces a number of new changes:
- Services are now inserted into redis with a prefix prepended to the
key name. This allows for easier filtering to get only live instances.
- The home page now uses an eex template for displaying all live
instances for every service, determined by the last update
- A "last_updated" field was added
- farside.ex was added to contain all functionality related to querying
for instances (WIP)
- Other improvements

lib/farside.ex

@@ -0,0 +1,45 @@
+defmodule Farside do
+  @service_prefix Application.fetch_env!(:farside, :service_prefix)
+
+  def get_services_map do
+    {:ok, redis_keys} = Redix.command(:redix, ["KEYS", "*"])
+
+    # Extract only service related keys
+    service_list =
+      Enum.filter(
+        redis_keys,
+        fn key ->
+          String.starts_with?(key, @service_prefix)
+        end
+      )
+
+    # Match service name to list of available instances
+    Enum.reduce(service_list, %{}, fn service, acc ->
+      {:ok, instance_list} =
+        Redix.command(
+          :redix,
+          ["LRANGE", service, "0", "-1"]
+        )
+
+      Map.put(
+        acc,
+        String.replace_prefix(
+          service,
+          @service_prefix,
+          ""
+        ),
+        instance_list
+      )
+    end)
+  end
+
+  def get_last_updated do
+    {:ok, last_updated} =
+      Redix.command(
+        :redix,
+        ["GET", "last_updated"]
+      )
+
+    last_updated
+  end
+end

lib/farside/router.ex

@@ -1,5 +1,7 @@
 defmodule Farside.Router do
+  @index Application.fetch_env!(:farside, :index)
   @fallback_str Application.fetch_env!(:farside, :fallback_str)
+  @service_prefix Application.fetch_env!(:farside, :service_prefix)
 
   use Plug.Router
 
@@ -7,7 +9,14 @@ defmodule Farside.Router do
   plug(:dispatch)
 
   get "/" do
-    send_resp(conn, 200, "")
+    resp =
+      EEx.eval_file(
+        @index,
+        last_updated: Farside.get_last_updated(),
+        services: Farside.get_services_map()
+      )
+
+    send_resp(conn, 200, resp)
   end
 
   get "/ping" do
@@ -22,7 +31,12 @@ defmodule Farside.Router do
     {:ok, instances} =
       Redix.command(
         :redix,
-        ["LRANGE", service, "0", "-1"]
+        [
+          "LRANGE",
+          "#{@service_prefix}#{service}",
+          "0",
+          "-1"
+        ]
       )
 
     # Either pick a random available instance,