Add prometheus metric to measure hub startup time (#2799)

Add prometheus metric to measure hub startup time

jupyterhub/app.py

@@ -85,6 +85,8 @@ from .utils import (
     print_ps_info,
     make_ssl_context,
 )
+from .metrics import HUB_STARTUP_DURATION_SECONDS
+from .metrics import INIT_SPAWNERS_DURATION_SECONDS
 from .metrics import RUNNING_SERVERS
 from .metrics import TOTAL_USERS
 
@@ -2220,6 +2222,7 @@ class JupyterHub(Application):
 
     @catch_config_error
     async def initialize(self, *args, **kwargs):
+        hub_startup_start_time = time.perf_counter()
         super().initialize(*args, **kwargs)
         if self.generate_config or self.generate_certs or self.subapp:
             return
@@ -2292,14 +2295,20 @@ class JupyterHub(Application):
 
         def log_init_time(f):
             n_spawners = f.result()
+            spawner_initialization_time = time.perf_counter() - init_start_time
+            INIT_SPAWNERS_DURATION_SECONDS.observe(spawner_initialization_time)
             self.log.info(
                 "Initialized %i spawners in %.3f seconds",
                 n_spawners,
-                time.perf_counter() - init_start_time,
+                spawner_initialization_time,
             )
 
         init_spawners_future.add_done_callback(log_init_time)
 
+        HUB_STARTUP_DURATION_SECONDS.observe(
+            time.perf_counter() - hub_startup_start_time
+        )
+
         try:
 
             # don't allow a zero timeout because we still need to be sure

jupyterhub/metrics.py

@@ -45,6 +45,14 @@ CHECK_ROUTES_DURATION_SECONDS = Histogram(
     'check_routes_duration_seconds', 'Time taken to validate all routes in proxy'
 )
 
+HUB_STARTUP_DURATION_SECONDS = Histogram(
+    'hub_startup_duration_seconds', 'Time taken for Hub to start'
+)
+
+INIT_SPAWNERS_DURATION_SECONDS = Histogram(
+    'init_spawners_duration_seconds', 'Time taken for spawners to initialize'
+)
+
 PROXY_POLL_DURATION_SECONDS = Histogram(
     'proxy_poll_duration_seconds', 'duration for polling all routes from proxy'
 )