feat: add GraphQL subscriptions and GraphiQL dev playground

Wire up real-time GraphQL subscriptions over WebSocket using
absinthe_phoenix for rollout progress, node status, and alert
state changes. Add GraphiQL playground at /dev/graphiql for
development.

Author: raffaelschneider

lib/sentinel_cp/application.ex

@@ -21,7 +21,9 @@ defmodule SentinelCp.Application do
       # Background job processing
       {Oban, Application.fetch_env!(:sentinel_cp, Oban)},
       # Start to serve requests, typically the last entry
-      SentinelCpWeb.Endpoint
+      SentinelCpWeb.Endpoint,
+      # GraphQL subscriptions (must start after Endpoint)
+      {Absinthe.Subscription, SentinelCpWeb.Endpoint}
     ]
 
     # See https://hexdocs.pm/elixir/Supervisor.html

lib/sentinel_cp/nodes.ex

@@ -126,6 +126,12 @@ defmodule SentinelCp.Nodes do
         end
       end
 
+      Absinthe.Subscription.publish(
+        SentinelCpWeb.Endpoint,
+        updated_node,
+        node_status: updated_node.project_id
+      )
+
       updated_node
     end)
   end

lib/sentinel_cp/observability/alert_evaluator.ex

@@ -191,7 +191,10 @@ defmodule SentinelCp.Observability.AlertEvaluator do
           alert_state
           |> AlertState.changeset(%{state: "firing", firing_at: now, value: value})
           |> Repo.update()
-          |> tap(fn {:ok, _} -> send_alert_notification(rule, value) end)
+          |> tap(fn {:ok, state} ->
+            send_alert_notification(rule, value)
+            publish_alert_state(state, rule)
+          end)
         else
           # Still pending, update value
           alert_state
@@ -216,6 +219,10 @@ defmodule SentinelCp.Observability.AlertEvaluator do
         alert_state
         |> AlertState.changeset(%{state: "resolved", resolved_at: now})
         |> Repo.update()
+        |> tap(fn {:ok, updated} ->
+          rule = Repo.get(AlertRule, updated.alert_rule_id)
+          if rule, do: publish_alert_state(updated, rule)
+        end)
 
       _ ->
         :ok
@@ -236,9 +243,18 @@ defmodule SentinelCp.Observability.AlertEvaluator do
       |> Repo.insert()
 
     send_alert_notification(rule, value)
+    publish_alert_state(state, rule)
     {:ok, state}
   end
 
+  defp publish_alert_state(alert_state, rule) do
+    Absinthe.Subscription.publish(
+      SentinelCpWeb.Endpoint,
+      alert_state,
+      alert_state: rule.project_id
+    )
+  end
+
   defp send_alert_notification(rule, value) do
     Logger.warning("Alert firing: #{rule.name} (#{rule.severity}) — value: #{value}")
 

lib/sentinel_cp/rollouts.ex

@@ -1427,6 +1427,8 @@ defmodule SentinelCp.Rollouts do
       "rollouts:#{rollout.project_id}",
       {:rollout_updated, rollout.id}
     )
+
+    Absinthe.Subscription.publish(SentinelCpWeb.Endpoint, rollout, rollout_progress: rollout.id)
   end
 
   defp broadcast_and_notify(rollout, old_state, new_state) do

lib/sentinel_cp_web/endpoint.ex

@@ -1,5 +1,6 @@
 defmodule SentinelCpWeb.Endpoint do
   use Phoenix.Endpoint, otp_app: :sentinel_cp
+  use Absinthe.Phoenix.Endpoint
 
   # The session will be stored in the cookie and signed,
   # this means its contents can be read but not tampered with.
@@ -15,6 +16,10 @@ defmodule SentinelCpWeb.Endpoint do
     websocket: [connect_info: [session: @session_options]],
     longpoll: [connect_info: [session: @session_options]]
 
+  socket "/api/v1/graphql/websocket", SentinelCpWeb.GraphQL.Socket,
+    websocket: true,
+    longpoll: false
+
   # Serve at "/" the static files from "priv/static" directory.
   #
   # When code reloading is disabled (e.g., in production),

lib/sentinel_cp_web/graphql/schema.ex

@@ -10,6 +10,7 @@ defmodule SentinelCpWeb.GraphQL.Schema do
   import_types(SentinelCpWeb.GraphQL.Types.Rollout)
   import_types(SentinelCpWeb.GraphQL.Types.Observability)
   import_types(SentinelCpWeb.GraphQL.Types.Policy)
+  import_types(SentinelCpWeb.GraphQL.Types.Subscription)
 
   query do
     import_fields(:project_queries)
@@ -26,6 +27,10 @@ defmodule SentinelCpWeb.GraphQL.Schema do
     import_fields(:rollout_mutations)
   end
 
+  subscription do
+    import_fields(:subscription_fields)
+  end
+
   def middleware(middleware, _field, %Absinthe.Type.Object{identifier: identifier})
       when identifier in [:query, :mutation] do
     [SentinelCpWeb.GraphQL.Middleware.AuthScope | middleware]

lib/sentinel_cp_web/graphql/socket.ex

@@ -0,0 +1,38 @@
+defmodule SentinelCpWeb.GraphQL.Socket do
+  @moduledoc false
+  use Phoenix.Socket
+  use Absinthe.Phoenix.Socket, schema: SentinelCpWeb.GraphQL.Schema
+
+  alias SentinelCp.Accounts
+
+  @impl true
+  def connect(%{"token" => token}, socket, _connect_info) do
+    case Accounts.get_api_key_by_key(token) do
+      nil ->
+        :error
+
+      api_key ->
+        Accounts.touch_api_key(api_key)
+
+        socket =
+          Absinthe.Phoenix.Socket.put_options(socket,
+            context: %{current_api_key: api_key}
+          )
+
+        {:ok, socket}
+    end
+  end
+
+  def connect(_params, _socket, _connect_info), do: :error
+
+  @impl true
+  def id(socket) do
+    case socket.assigns[:absinthe] do
+      %{opts: [context: %{current_api_key: api_key}]} ->
+        "graphql:#{api_key.id}"
+
+      _ ->
+        nil
+    end
+  end
+end

lib/sentinel_cp_web/graphql/types/observability.ex

@@ -22,6 +22,15 @@ defmodule SentinelCpWeb.GraphQL.Types.Observability do
     field :error_budget_remaining, :float
   end
 
+  object :alert_state do
+    field :id, non_null(:id)
+    field :state, non_null(:string)
+    field :value, :float
+    field :started_at, :datetime
+    field :firing_at, :datetime
+    field :resolved_at, :datetime
+  end
+
   object :observability_queries do
     field :alert_rules, list_of(:alert_rule) do
       arg(:project_id, non_null(:id))

lib/sentinel_cp_web/graphql/types/subscription.ex

@@ -0,0 +1,21 @@
+defmodule SentinelCpWeb.GraphQL.Types.Subscription do
+  @moduledoc false
+  use Absinthe.Schema.Notation
+
+  object :subscription_fields do
+    field :rollout_progress, :rollout do
+      arg(:rollout_id, non_null(:id))
+      config(fn args, _ -> {:ok, topic: args.rollout_id} end)
+    end
+
+    field :node_status, :sentinel_node do
+      arg(:project_id, non_null(:id))
+      config(fn args, _ -> {:ok, topic: args.project_id} end)
+    end
+
+    field :alert_state, :alert_state do
+      arg(:project_id, non_null(:id))
+      config(fn args, _ -> {:ok, topic: args.project_id} end)
+    end
+  end
+end

lib/sentinel_cp_web/router.ex

@@ -773,5 +773,12 @@ defmodule SentinelCpWeb.Router do
       live_dashboard "/dashboard", metrics: SentinelCpWeb.Telemetry
       forward "/mailbox", Plug.Swoosh.MailboxPreview
     end
+
+    scope "/dev" do
+      forward "/graphiql", Absinthe.Plug.GraphiQL,
+        schema: SentinelCpWeb.GraphQL.Schema,
+        socket: SentinelCpWeb.GraphQL.Socket,
+        json_codec: Jason
+    end
   end
 end