application: use EventletTimeoutMiddleware if using eventlet

also catch EventletTimeout exceptions, turning these into 504s,
which are the closest thing to an application timeout standard
codes seem to cover

60s timeout to start with as this matches our cloudfront/ALB
timeouts and so should present the same behaviour to external
users

app/__init__.py

@@ -27,6 +27,7 @@
 from notifications_utils.clients.signing.signing_client import Signing
 from notifications_utils.clients.statsd.statsd_client import StatsdClient
 from notifications_utils.clients.zendesk.zendesk_client import ZendeskClient
+from notifications_utils.eventlet import EventletTimeout
 from notifications_utils.local_vars import LazyLocalGetter
 from sqlalchemy import event
 from werkzeug.exceptions import HTTPException as WerkzeugHTTPException
@@ -420,6 +421,11 @@ def exception(error):
         code = getattr(error, "code", 500)
         return jsonify(result="error", message=msg), code
 
+    @app.errorhandler(EventletTimeout)
+    def eventlet_timeout(error):
+        app.logger.exception(error)
+        return jsonify(result="error", message="Timeout serving request"), 504
+
     @app.errorhandler(WerkzeugHTTPException)
     def werkzeug_exception(e):
         return make_response(jsonify(result="error", message=e.description), e.code, e.get_headers())

application.py

@@ -6,6 +6,11 @@
 from app import create_app  # noqa
 from app.notify_api_flask_app import NotifyApiFlaskApp  # noqa
 
+from notifications_utils.eventlet import EventletTimeoutMiddleware, using_eventlet  # noqa
+
 application = NotifyApiFlaskApp("app")
 
 create_app(application)
+
+if using_eventlet:
+    application = EventletTimeoutMiddleware(application, timeout_seconds=60)