Add Healthcheck Endpoint for Service Monitoring (#2248)

#### What problem does this PR solve?

This PR introduces a new `GET /healthcheck` endpoint to provide a
standard mechanism for monitoring the application's health and
availability. This is a common requirement for running services in
production, allowing load balancers, container orchestrators (like
Kubernetes), and other monitoring tools to verify that the application
is running and responsive.

#### What is the solution?

1.  **New Endpoint:** A `GET /healthcheck` route has been added.
2.  **Response:** The endpoint returns a JSON response containing:
    *   `status`: Always `"ok"` to indicate the service is running.
* `build`: The git revision hash of the current build. This provides
essential diagnostic information for debugging and tracking deployed
versions without exposing sensitive system details.
3. **API Documentation:** The new endpoint is fully documented using
`OpenApiSpex`, and the specification is available via the Swagger UI.
4. **Testing:** A new test suite has been added to verify the endpoint's
functionality.

This approach provides a simple, fast, and secure liveness probe while
still offering valuable, non-sensitive build information.

Co-authored-by: Nate Shoemaker <[email protected]>

Author: taras-tyshko

.cspell.json

@@ -146,6 +146,7 @@
     "undigits",
     "unprovisioned",
     "validtoken",
-    "xdelta"
+    "xdelta",
+    "healthcheck"
   ]
 }

lib/nerves_hub_web/controllers/healthcheck_controller.ex

@@ -0,0 +1,40 @@
+defmodule NervesHubWeb.HealthcheckController do
+  use NervesHubWeb, :controller
+  use OpenApiSpex.ControllerSpecs
+
+  alias OpenApiSpex.Schema
+
+  defmodule HealthcheckResponse do
+    require OpenApiSpex
+
+    OpenApiSpex.schema(%{
+      title: "Healthcheck Response",
+      description: "The response from the healthcheck endpoint.",
+      type: :object,
+      properties: %{
+        status: %Schema{
+          type: :string,
+          description: "The operational status of the service.",
+          example: "ok"
+        },
+        build: %Schema{
+          type: :string,
+          description: "The git revision of the build.",
+          example: "e35ffc5"
+        }
+      },
+      required: [:status, :build]
+    })
+  end
+
+  operation(:index,
+    description: "Check the health of the service.",
+    summary: "Healthcheck",
+    tags: ["Monitoring"],
+    responses: %{200 => {"OK", "application/json", HealthcheckResponse}}
+  )
+
+  def index(conn, _params) do
+    json(conn, %{status: "ok", build: System.build_info()[:revision]})
+  end
+end

lib/nerves_hub_web/router.ex

@@ -79,6 +79,11 @@ defmodule NervesHubWeb.Router do
     plug(NervesHubWeb.API.Plugs.Device)
   end
 
+  scope "/" do
+    pipe_through(:api)
+    get("/healthcheck", NervesHubWeb.HealthcheckController, :index)
+  end
+
   scope "/api" do
     pipe_through(:api)
     get("/openapi", OpenApiSpex.Plug.RenderSpec, [])

test/nerves_hub_web/controllers/healthcheck_controller_test.exs

@@ -0,0 +1,11 @@
+defmodule NervesHubWeb.HealthcheckControllerTest do
+  use NervesHubWeb.ConnCase, async: true
+
+  describe "GET /healthcheck" do
+    test "returns status and build information", %{conn: conn} do
+      conn = get(conn, ~p"/healthcheck")
+      response = json_response(conn, 200)
+      assert response == %{"status" => "ok", "build" => System.build_info()[:revision]}
+    end
+  end
+end