chore(backend): move services to horde

Moves relevant registries and supervisors in the application tree to allow
edgehog to scale horizontally. This is done only with registries and supervsors
where it makes sens to chare the load:

- `Containers.Reconciler`, where the process spawns per-tenant and talks with
  the DB.
- `Tenant.Reconciler`, where tasks and processes are again spawned per-tenant.
- `Devices.Reconciler` is moved to a single process managed trough a horde
  process to make it single per-cluster.

Signed-off-by: Luca Zaninotto <luca.zaninotto@secomind.com>

Author: lusergit

backend/lib/edgehog/application.ex

@@ -68,7 +68,8 @@ defmodule Edgehog.Application do
       {Edgehog.Tenants.Reconciler.Supervisor,
        tenant_to_trigger_url_fun: tenant_to_trigger_url_fun},
       # Start Containers reconciler
-      {Registry, keys: :unique, name: Edgehog.Containers.Reconciler.Registry},
+      {Horde.Registry, keys: :unique, name: Edgehog.Containers.Reconciler.Registry},
+      {Horde.Registry, keys: :unique, name: Edgehog.Devices.Reconciler.Registry},
       # Start the Endpoint (http/https)
       Endpoint,
       # Fetch Astarte devices

backend/lib/edgehog/containers/reconciler/reconciler.ex

@@ -144,7 +144,7 @@ defmodule Edgehog.Containers.Reconciler do
   end
 
   defp name(tenant) do
-    {:via, Registry, {Edgehog.Containers.Reconciler.Registry, tenant.tenant_id}}
+    {:via, Horde.Registry, {Edgehog.Containers.Reconciler.Registry, tenant.tenant_id}}
   end
 
   defp do_register_device(device, state) do

backend/lib/edgehog/devices/reconciler/reconciler.ex

@@ -28,7 +28,7 @@ defmodule Edgehog.Devices.Reconciler do
   require Logger
 
   def start_link(opts \\ []) do
-    GenServer.start_link(__MODULE__, opts, name: __MODULE__)
+    GenServer.start_link(__MODULE__, opts, name: name())
   end
 
   @impl GenServer
@@ -79,10 +79,36 @@ defmodule Edgehog.Devices.Reconciler do
     {:noreply, state}
   end
 
+  @impl GenServer
+  def handle_info({:EXIT, _pid, {:name_conflict, {_name, _value}, _registry, _winning_pid}}, state) do
+    _ =
+      Logger.warning(
+        "Received a :name_conflict signal from the outer space, maybe a netsplit occurred? Gracefully shutting down.",
+        tag: "RPC exit"
+      )
+
+    {:stop, :shutdown, state}
+  end
+
+  @impl GenServer
+  def handle_info({:EXIT, _pid, :shutdown}, state) do
+    _ =
+      Logger.warning(
+        "Received a :shutdown signal from the outer space, maybe the supervisor is mad? Gracefully shutting down.",
+        tag: "RPC exit"
+      )
+
+    {:stop, :shutdown, state}
+  end
+
   defp spawn_reconciliation_task(tenant) do
     Task.Supervisor.async(Reconciler.Supervisor, fn ->
       Logger.info("Reconciling tenant #{tenant.slug}")
       Reconciler.Core.reconcile(tenant)
     end)
   end
+
+  defp name do
+    {:via, Horde.Registry, {Edgehog.Devices.Reconciler.Registry, :auto}}
+  end
 end

backend/test/edgehog_web/controllers/astarte_trigger_controller/device_events_test.exs

@@ -304,7 +304,7 @@ defmodule EdgehogWeb.Controllers.AstarteTriggerController.DeviceEventsTest do
       timestamp = utc_now_second()
       event = disconnection_trigger(device.device_id, timestamp)
 
-      Registry.register(Edgehog.Containers.Reconciler.Registry, tenant.tenant_id, self())
+      Horde.Registry.register(Edgehog.Containers.Reconciler.Registry, tenant.tenant_id, self())
 
       stub(DeviceStatusMock, :get, fn _client, _device_id -> flunk() end)
       assert conn |> post(path, event) |> response(200)