Add a cache module for the API main endpoint

apps/transport/lib/transport/api_cache.ex

@@ -0,0 +1,46 @@
+defmodule Transport.APICache do
+  @moduledoc """
+  A module that populates the Cachex cache for the /api/datasets endpoint ("api-datasets-index")
+  """
+
+  use GenServer
+  require Logger
+
+  @job_delay :timer.seconds(300)
+  @cache_ttl :timer.seconds(600)
+
+  def start_link(_opts) do
+    GenServer.start_link(__MODULE__, %{})
+  end
+
+  def init(state) do
+    # initial schedule is immediate, but via the same code path,
+    # to ensure we jump on the data
+    schedule_next_occurrence(0)
+
+    {:ok, state}
+  end
+
+  def schedule_next_occurrence(delay \\ @job_delay) do
+    Process.send_after(self(), :tick, delay)
+  end
+
+  def handle_info(:tick, state) do
+    schedule_next_occurrence()
+    populate_cache()
+    {:noreply, state}
+  end
+
+  def populate_cache do
+    Logger.info("[api-cache-genserver] Populating cache for /api/datasets…")
+
+    Cachex.put(
+      Transport.Application.cache_name(),
+      "api-datasets-index",
+      TransportWeb.API.DatasetController.prepare_datasets_index_data(),
+      ttl: @cache_ttl
+    )
+
+    Logger.info("[api-cache-genserver] Finished populating cache for /api/datasets")
+  end
+end

apps/transport/lib/transport/application.ex

@@ -24,7 +24,7 @@ defmodule Transport.Application do
       end
     end
 
-    run_realtime_poller = webserver_enabled?() && Mix.env() != :test
+    run_web_processes = webserver_enabled?() && Mix.env() != :test
 
     children =
       [
@@ -43,7 +43,8 @@ defmodule Transport.Application do
         Transport.Vault
       ]
       |> add_scheduler()
-      |> add_if(fn -> run_realtime_poller end, Transport.RealtimePoller)
+      |> add_if(fn -> run_web_processes end, Transport.RealtimePoller)
+      |> add_if(fn -> run_web_processes end, Transport.APICache)
       ## manually add a children supervisor that is not scheduled
       |> Kernel.++([{Task.Supervisor, name: ImportTaskSupervisor}])
 

apps/transport/lib/transport_web/api/controllers/datasets_controller.ex

@@ -9,7 +9,7 @@ defmodule TransportWeb.API.DatasetController do
   # The default (one minute) felt a bit too high for someone doing scripted operations
   # (have to wait during experimentations), so I lowered it a bit. It is high enough
   # that it will still protect a lot against excessive querying.
-  @cache_ttl :timer.seconds(30)
+  @cache_ttl :timer.seconds(600)
 
   @spec open_api_operation(any) :: Operation.t()
   def open_api_operation(action), do: apply(__MODULE__, :"#{action}_operation", [])