Issue #13 Outreachy: add running_servers metric

jupyterhub/handlers/base.py

@@ -31,6 +31,7 @@ from ..utils import maybe_future, url_path_join
 from ..metrics import (
     SERVER_SPAWN_DURATION_SECONDS, ServerSpawnStatus,
     PROXY_ADD_DURATION_SECONDS, ProxyAddStatus,
+    CURRENTLY_RUNNING_SERVERS
 )
 
 # pattern for the authentication token header
@@ -729,6 +730,7 @@ class BaseHandler(RequestHandler):
             toc = IOLoop.current().time()
             self.log.info("User %s took %.3f seconds to start", user_server_name, toc-tic)
             self.statsd.timing('spawner.success', (toc - tic) * 1000)
+            CURRENTLY_RUNNING_SERVERS.inc()
             SERVER_SPAWN_DURATION_SECONDS.labels(
                 status=ServerSpawnStatus.success
             ).observe(time.perf_counter() - spawn_start_time)
@@ -880,6 +882,7 @@ class BaseHandler(RequestHandler):
             toc = IOLoop.current().time()
             self.log.info("User %s server took %.3f seconds to stop", user.name, toc - tic)
             self.statsd.timing('spawner.stop', (toc - tic) * 1000)
+            CURRENTLY_RUNNING_SERVERS.dec()
 
         try:
             await gen.with_timeout(timedelta(seconds=self.slow_stop_timeout), stop())

jupyterhub/metrics.py

@@ -18,6 +18,7 @@ them manually here.
 from enum import Enum
 
 from prometheus_client import Histogram
+from prometheus_client import Gauge
 
 REQUEST_DURATION_SECONDS = Histogram(
     'request_duration_seconds',
@@ -34,6 +35,13 @@ SERVER_SPAWN_DURATION_SECONDS = Histogram(
     buckets=[0.5, 1, 2.5, 5, 10, 15, 30, 60, 120, float("inf")]
 )
 
+CURRENTLY_RUNNING_SERVERS = Gauge(
+    'currently_running_servers',
+    'the number of user servers currently running',
+)
+
+CURRENTLY_RUNNING_SERVERS.set(0)
+
 class ServerSpawnStatus(Enum):
     """
     Possible values for 'status' label of SERVER_SPAWN_DURATION_SECONDS