Remove Redis dep, replace w/ native Elixir lib

This removes the dependency on Redis for core app functionality. Rather
than using the key/value store provided by Redis, Farside now uses a
key/val store provided by [cubdb](https://github.com/lucaong/cubdb) for
identical functionality but without reliance on a non-Elixir service.

This solution was chosen instead of ets, because storing instance data
in memory leads to a period of broken functionality whenever the app
restarts and hasn't re-populated instance data yet. It was also chosen
instead of dets, because the documentation for dets was pretty hard to
understand at first glance.

Tests and the CI build were updated to reflect the removed dependency on
Redis.

New environment variable `FARSIDE_DATA_DIR` can be used to point to a
directory where the instance data can be stored by cubdb.

Co-authored-by: Jason Clark <mithereal@gmail.com>

lib/farside/application.ex

@@ -1,16 +1,13 @@
 defmodule Farside.Application do
-  #@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)
+    data_dir = Application.fetch_env!(:farside, :data_dir)
     IO.puts "Running on http://localhost:#{farside_port}"
-    IO.puts "Redis conn: #{redis_conn}"
 
     children = [
       Plug.Cowboy.child_spec(
@@ -21,7 +18,7 @@ defmodule Farside.Application do
         ]
       ),
       {PlugAttack.Storage.Ets, name: Farside.Throttle.Storage, clean_period: 60_000},
-      {Redix, {redis_conn, [name: :redix]}},
+      {CubDB, [data_dir: data_dir, name: CubDB]},
       Farside.Scheduler,
       Farside.Server
     ]

lib/farside/instances.ex

@@ -12,11 +12,7 @@ defmodule Farside.Instances do
     update()
 
     # Add UTC time of last update
-    Redix.command(:redix, [
-      "SET",
-      "last_updated",
-      Calendar.strftime(DateTime.utc_now(), "%c")
-    ])
+    CubDB.put(CubDB, "last_updated", Calendar.strftime(DateTime.utc_now(), "%c"))
   end
 
   def request(url) do
@@ -69,41 +65,24 @@ defmodule Farside.Instances do
           request(request_url) == :good
         end)
 
-      add_to_redis(service, result)
+      add_to_db(service, result)
       log_results(service.type, result)
     end
   end
 
-  def add_to_redis(service, instances) do
+  def add_to_db(service, instances) do
     # Remove previous list of instances
-    Redix.command(:redix, [
-      "DEL",
-      "#{@service_prefix}#{service.type}"
-    ])
+    CubDB.delete(CubDB, "#{@service_prefix}#{service.type}")
 
     # Update with new list of available instances
-    Redix.command(
-      :redix,
-      [
-        "LPUSH",
-        "#{@service_prefix}#{service.type}"
-      ] ++ instances
-    )
+    CubDB.put(CubDB, "#{@service_prefix}#{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(:redix, [
-        "SET",
-        "#{service.type}#{@fallback_suffix}",
-        Enum.random(instances)
-      ])
+      CubDB.put(CubDB, "#{service.type}#{@fallback_suffix}", Enum.random(instances))
     else
-      Redix.command(:redix, [
-        "SET",
-        "#{service.type}#{@fallback_suffix}",
-        service.fallback
-      ])
+      CubDB.put(CubDB, "#{service.type}#{@fallback_suffix}", service.fallback)
     end
   end
 

lib/farside/router.ex

@@ -29,12 +29,6 @@ defmodule Farside.Router do
     send_resp(conn, 200, resp)
   end
 
-  get "/ping" do
-    # Useful for app healthcheck
-    {:ok, resp} = Redix.command(:redix, ["PING"])
-    send_resp(conn, 200, resp)
-  end
-
   get "/_/:service/*glob" do
     r_path = String.slice(conn.request_path, 2..-1)