Allow disabling the Preview queue consumer

config/config.exs

@@ -4,6 +4,7 @@ config :preview,
   queue_id: "dummy",
   queue_producer: Broadway.DummyProducer,
   queue_concurrency: 2,
+  queue_enabled: true,
   package_store_impl: Preview.Package.DefaultStore,
   package_updater_impl: Preview.Package.Updater,
   hex_impl: Preview.Hex.HTTP,

config/runtime.exs

@@ -1,18 +1,39 @@
 import Config
 
 if config_env() == :prod do
+  queue_enabled =
+    case System.get_env("PREVIEW_QUEUE_ENABLED", "true") do
+      "true" ->
+        true
+
+      "false" ->
+        false
+
+      value ->
+        raise "invalid PREVIEW_QUEUE_ENABLED #{inspect(value)}; expected \"true\" or \"false\""
+    end
+
   config :preview,
     host: System.fetch_env!("PREVIEW_HOST"),
     repo_url: System.fetch_env!("PREVIEW_REPO_URL"),
     repo_public_key: System.fetch_env!("PREVIEW_REPO_PUBLIC_KEY"),
-    queue_id: System.fetch_env!("PREVIEW_QUEUE_ID"),
-    queue_concurrency: String.to_integer(System.fetch_env!("PREVIEW_QUEUE_CONCURRENCY")),
-    fastly_key: System.fetch_env!("PREVIEW_FASTLY_KEY"),
-    fastly_repo: System.fetch_env!("PREVIEW_FASTLY_REPO")
+    queue_enabled: queue_enabled
 
-  config :preview, :repo_bucket,
-    implementation: Preview.Storage.S3,
-    name: System.fetch_env!("PREVIEW_REPO_BUCKET")
+  if queue_enabled do
+    config :preview,
+      queue_id: System.fetch_env!("PREVIEW_QUEUE_ID"),
+      queue_concurrency: String.to_integer(System.fetch_env!("PREVIEW_QUEUE_CONCURRENCY")),
+      fastly_key: System.fetch_env!("PREVIEW_FASTLY_KEY"),
+      fastly_repo: System.fetch_env!("PREVIEW_FASTLY_REPO")
+
+    config :preview, :repo_bucket,
+      implementation: Preview.Storage.S3,
+      name: System.fetch_env!("PREVIEW_REPO_BUCKET")
+
+    config :ex_aws,
+      access_key_id: System.fetch_env!("PREVIEW_AWS_ACCESS_KEY_ID"),
+      secret_access_key: System.fetch_env!("PREVIEW_AWS_ACCESS_KEY_SECRET")
+  end
 
   config :preview, :preview_bucket,
     implementation: Preview.Storage.GCS,
@@ -23,10 +44,6 @@ if config_env() == :prod do
     url: [host: System.fetch_env!("PREVIEW_HOST")],
     secret_key_base: System.fetch_env!("PREVIEW_SECRET_KEY_BASE")
 
-  config :ex_aws,
-    access_key_id: System.fetch_env!("PREVIEW_AWS_ACCESS_KEY_ID"),
-    secret_access_key: System.fetch_env!("PREVIEW_AWS_ACCESS_KEY_SECRET")
-
   config :sentry,
     dsn: System.fetch_env!("PREVIEW_SENTRY_DSN"),
     environment_name: System.fetch_env!("PREVIEW_ENV")

lib/preview/application.ex

@@ -9,23 +9,26 @@ defmodule Preview.Application do
     :logger.add_handler(:my_sentry_handler, Sentry.LoggerHandler, %{})
     setup_tmp_dir()
 
-    children = [
+    children = children(Application.fetch_env!(:preview, :queue_enabled))
+
+    opts = [strategy: :one_for_one, name: Preview.Supervisor]
+    Supervisor.start_link(children, opts)
+  end
+
+  def children(queue_enabled) when is_boolean(queue_enabled) do
+    common = [
       Preview.TmpDir,
       PreviewWeb.Telemetry,
       {Phoenix.PubSub, name: Preview.PubSub},
       {Task.Supervisor, name: Preview.Tasks},
       {Finch, name: Preview.Finch, pools: finch_pools()},
       goth_spec(),
-      {Preview.Debouncer, name: Preview.Debouncer},
-      Preview.Queue,
       PreviewWeb.Endpoint,
       package_spec()
     ]
 
-    # See https://hexdocs.pm/elixir/Supervisor.html
-    # for other strategies and supported options
-    opts = [strategy: :one_for_one, name: Preview.Supervisor]
-    Supervisor.start_link(children, opts)
+    queue = [{Preview.Debouncer, name: Preview.Debouncer}, Preview.Queue]
+    common ++ if(queue_enabled, do: queue, else: [])
   end
 
   # Tell Phoenix to update the endpoint configuration

test/preview/application_test.exs

@@ -0,0 +1,124 @@
+defmodule Preview.ApplicationTest do
+  use ExUnit.Case, async: true
+
+  alias Preview.Application
+
+  test "queue children can be disabled without removing the web endpoint" do
+    enabled = child_ids(Application.children(true))
+    disabled = child_ids(Application.children(false))
+
+    assert Preview.Queue in enabled
+    assert Preview.Debouncer in enabled
+    refute Preview.Queue in disabled
+    refute Preview.Debouncer in disabled
+    assert PreviewWeb.Endpoint in enabled
+    assert PreviewWeb.Endpoint in disabled
+  end
+
+  test "disabled production configuration does not require queue credentials" do
+    elixir = System.find_executable("elixir")
+    erl = System.find_executable("erl")
+    path = [Path.dirname(elixir), Path.dirname(erl), "/usr/bin", "/bin"] |> Enum.uniq()
+
+    env = [
+      "PATH=#{Enum.join(path, ":")}",
+      "PREVIEW_QUEUE_ENABLED=false",
+      "PREVIEW_HOST=preview.hex.pm",
+      "PREVIEW_REPO_URL=https://repo.hex.pm",
+      "PREVIEW_REPO_PUBLIC_KEY=public-key",
+      "PREVIEW_BUCKET=preview-bucket",
+      "PREVIEW_PORT=4005",
+      "PREVIEW_SECRET_KEY_BASE=secret-key-base",
+      "PREVIEW_SENTRY_DSN=sentry-dsn",
+      "PREVIEW_ENV=prod",
+      "BEAM_PORT=14005"
+    ]
+
+    expression = ~S|Config.Reader.read!("config/runtime.exs", env: :prod); IO.write("configured")|
+
+    assert {"configured", 0} =
+             System.cmd(System.find_executable("env"), ["-i" | env] ++ [elixir, "-e", expression])
+  end
+
+  test "production configuration defaults to an enabled queue" do
+    env = runtime_env() ++ queue_env()
+
+    expression =
+      ~S"""
+      config = Config.Reader.read!("config/runtime.exs", env: :prod)
+      preview = config[:preview]
+      ex_aws = config[:ex_aws]
+
+      IO.write(
+        Enum.join(
+          [
+            preview[:queue_id],
+            preview[:queue_concurrency],
+            preview[:fastly_key],
+            preview[:fastly_repo],
+            preview[:repo_bucket][:name],
+            ex_aws[:access_key_id],
+            ex_aws[:secret_access_key]
+          ],
+          "|"
+        )
+      )
+      """
+
+    assert {"queue|10|fastly-key|fastly-repo|repo-bucket|aws-key|aws-secret", 0} =
+             System.cmd(
+               System.find_executable("env"),
+               ["-i" | env] ++ [System.find_executable("elixir"), "-e", expression]
+             )
+  end
+
+  test "production configuration rejects invalid queue settings" do
+    env = ["PREVIEW_QUEUE_ENABLED=invalid" | runtime_env()]
+    expression = ~S|Config.Reader.read!("config/runtime.exs", env: :prod)|
+
+    assert {output, status} =
+             System.cmd(
+               System.find_executable("env"),
+               ["-i" | env] ++ [System.find_executable("elixir"), "-e", expression],
+               stderr_to_stdout: true
+             )
+
+    assert status != 0
+    assert output =~ "invalid PREVIEW_QUEUE_ENABLED"
+  end
+
+  defp runtime_env do
+    elixir = System.find_executable("elixir")
+    erl = System.find_executable("erl")
+    path = [Path.dirname(elixir), Path.dirname(erl), "/usr/bin", "/bin"] |> Enum.uniq()
+
+    [
+      "PATH=#{Enum.join(path, ":")}",
+      "PREVIEW_HOST=preview.hex.pm",
+      "PREVIEW_REPO_URL=https://repo.hex.pm",
+      "PREVIEW_REPO_PUBLIC_KEY=public-key",
+      "PREVIEW_BUCKET=preview-bucket",
+      "PREVIEW_PORT=4005",
+      "PREVIEW_SECRET_KEY_BASE=secret-key-base",
+      "PREVIEW_SENTRY_DSN=sentry-dsn",
+      "PREVIEW_ENV=prod",
+      "BEAM_PORT=14005"
+    ]
+  end
+
+  defp queue_env do
+    [
+      "PREVIEW_QUEUE_ID=queue",
+      "PREVIEW_QUEUE_CONCURRENCY=10",
+      "PREVIEW_FASTLY_KEY=fastly-key",
+      "PREVIEW_FASTLY_REPO=fastly-repo",
+      "PREVIEW_REPO_BUCKET=repo-bucket",
+      "PREVIEW_AWS_ACCESS_KEY_ID=aws-key",
+      "PREVIEW_AWS_ACCESS_KEY_SECRET=aws-secret"
+    ]
+  end
+
+  defp child_ids(children) do
+    MapSet.new(children, fn child -> Supervisor.child_spec(child, []).id end)
+  end
+end