feat: Add /health endpoint for server monitoring

dash/dash.py

@@ -416,6 +416,10 @@ class Dash(ObsoleteChecker):
     :param use_async: When True, the app will create async endpoints, as a dev,
         they will be responsible for installing the `flask[async]` dependency.
     :type use_async: boolean
+
+    :param health_endpoint: Path for the health check endpoint. Set to None to
+        disable the health endpoint. Default is None.
+    :type health_endpoint: string or None
     """
 
     _plotlyjs_url: str
@@ -466,6 +470,7 @@ def __init__(  # pylint: disable=too-many-statements
         description: Optional[str] = None,
         on_error: Optional[Callable[[Exception], Any]] = None,
         use_async: Optional[bool] = None,
+        health_endpoint: Optional[str] = None,
         **obsolete,
     ):
 
@@ -537,6 +542,7 @@ def __init__(  # pylint: disable=too-many-statements
             update_title=update_title,
             include_pages_meta=include_pages_meta,
             description=description,
+            health_endpoint=health_endpoint,
         )
         self.config.set_read_only(
             [
@@ -769,6 +775,8 @@ def _setup_routes(self):
             self._add_url("_dash-update-component", self.dispatch, ["POST"])
         self._add_url("_reload-hash", self.serve_reload_hash)
         self._add_url("_favicon.ico", self._serve_default_favicon)
+        if self.config.health_endpoint is not None:
+            self._add_url(self.config.health_endpoint, self.serve_health)
         self._add_url("", self.index)
 
         if jupyter_dash.active:
@@ -987,6 +995,13 @@ def serve_reload_hash(self):
             }
         )
 
+    def serve_health(self):
+        """
+        Health check endpoint for monitoring Dash server status.
+        Returns a simple "OK" response with HTTP 200 status.
+        """
+        return flask.Response("OK", status=200, mimetype="text/plain")
+
     def get_dist(self, libraries: Sequence[str]) -> list:
         dists = []
         for dist_type in ("_js_dist", "_css_dist"):

tests/unit/test_health_endpoint_unit.py

@@ -0,0 +1,72 @@
+"""
+Tests for the health endpoint.
+
+Covers:
+- disabled by default
+- enabled returns plain OK 200
+- respects routes_pathname_prefix
+- custom nested path works
+- HEAD allowed, POST not allowed
+"""
+
+from dash import Dash, html
+
+
+def test_health_disabled_by_default_returns_404():
+    app = Dash(__name__)  # health_endpoint=None by default
+    app.layout = html.Div("Test")
+    client = app.server.test_client()
+    r = client.get("/health")
+    # When health endpoint is disabled, it returns the main page (200) instead of 404
+    # This is expected behavior - the health endpoint is not available
+    assert r.status_code == 200
+    # Should return HTML content, not "OK"
+    assert b"OK" not in r.data
+
+
+def test_health_enabled_returns_ok_200_plain_text():
+    app = Dash(__name__, health_endpoint="health")
+    app.layout = html.Div("Test")
+    client = app.server.test_client()
+
+    r = client.get("/health")
+    assert r.status_code == 200
+    assert r.data == b"OK"
+    # Flask automatically sets mimetype to text/plain for Response with mimetype
+    assert r.mimetype == "text/plain"
+
+
+def test_health_respects_routes_pathname_prefix():
+    app = Dash(__name__, routes_pathname_prefix="/x/", health_endpoint="health")
+    app.layout = html.Div("Test")
+    client = app.server.test_client()
+
+    ok = client.get("/x/health")
+    miss = client.get("/health")
+
+    assert ok.status_code == 200 and ok.data == b"OK"
+    assert miss.status_code == 404
+
+
+def test_health_custom_nested_path():
+    app = Dash(__name__, health_endpoint="api/v1/health")
+    app.layout = html.Div("Test")
+    client = app.server.test_client()
+
+    r = client.get("/api/v1/health")
+    assert r.status_code == 200
+    assert r.data == b"OK"
+
+
+def test_health_head_allowed_and_post_405():
+    app = Dash(__name__, health_endpoint="health")
+    app.layout = html.Div("Test")
+    client = app.server.test_client()
+
+    head = client.head("/health")
+    assert head.status_code == 200
+    # for HEAD the body can be empty, so we do not validate body
+    assert head.mimetype == "text/plain"
+
+    post = client.post("/health")
+    assert post.status_code == 405