NODE-2836 Separate Liveness check proc to not be blocked by requests to /metrics (#58)

* Separate Liveness check proc to not block requests

* rm test changes

* Test fixes

* Test fixes

* Linting changes

Author: rodgerjohnson

docker-compose.yml

@@ -12,6 +12,7 @@ services:
     build: .
     ports:
       - "8000:8000"
+      - "8001:8001"
     expose:
       - 8080
     networks:

src/exporter.py

@@ -1,9 +1,9 @@
 """Main module that loads Prometheus registry and starts a web-server."""
+import threading
 from wsgiref.simple_server import make_server
 from prometheus_client import REGISTRY, make_wsgi_app
 from metrics import PrometheusCustomCollector
 
-
 def return200(_, start_fn):
     """Wsgi http response function."""
     start_fn('200 OK', [])
@@ -21,16 +21,26 @@ def exporter(environ, start_fn):  # pylint: disable=inconsistent-return-statemen
     match environ['PATH_INFO']:
         case '/metrics':
             return metrics_app(environ, start_fn)
+        case _:
+            return return404(environ, start_fn)
+
+def liveness(environ, start_fn):
+    """Liveness endpoint function"""
+    match environ['PATH_INFO']:
         case '/readiness':
             return return200(environ, start_fn)
         case '/liveness':
             return return200(environ, start_fn)
-        case _:
-            return return404(environ, start_fn)
 
+def start_liveness():
+    """Liveness thread function"""
+    httpd_liveness = make_server('', 8001, liveness)
+    httpd_liveness.serve_forever()
 
 if __name__ == '__main__':
     REGISTRY.register(PrometheusCustomCollector())
     metrics_app = make_wsgi_app()
+    liveness_thread = threading.Thread(target=start_liveness)
+    liveness_thread.start()
     httpd = make_server('', 8000, exporter)
     httpd.serve_forever()

src/test_exporter.py

@@ -1,7 +1,7 @@
 """Tests the exporter module"""
 from unittest import TestCase, mock
 
-from exporter import return200, return404, exporter
+from exporter import return200, return404, exporter, liveness
 
 
 class TestExporter(TestCase):
@@ -35,15 +35,15 @@ def test_exporter_readiness(self):
         with the environ and HTTP response callable"""
         environ = {'PATH_INFO': '/readiness'}
         with mock.patch('exporter.return200') as mocked:
-            exporter(environ, self.start_fn_mock)
+            liveness(environ, self.start_fn_mock)
             mocked.assert_called_once_with(environ, self.start_fn_mock)
 
     def test_exporter_liveness(self):
         """Tests that the liveness path invokes return200
         with the environ and HTTP response callable"""
         environ = {'PATH_INFO': '/liveness'}
         with mock.patch('exporter.return200') as mocked:
-            exporter(environ, self.start_fn_mock)
+            liveness(environ, self.start_fn_mock)
             mocked.assert_called_once_with(environ, self.start_fn_mock)
 
     def test_exporter_404(self):