Allow users to opt out of prometheus metrics

Poor mans fix for jupyter-server#123

Author: dleen

README.md

@@ -91,6 +91,13 @@ As a command line argument:
 jupyter notebook --ResourceUseDisplay.track_cpu_percent=True
 ```
 
+### Disable Prometheus Metrics
+There is a [known bug](https://github.com/jupyter-server/jupyter-resource-usage/issues/123) with Prometheus metrics which
+causes "lag"/pauses in the UI. To fix this you can disable Prometheus metric reporting using:
+```
+--ResourceUseDisplay.enable_prometheus_metrics=False
+```
+
 ## Resources Displayed
 
 Currently the server extension only reports memory usage (just RSS) and CPU usage. Other metrics will be

jupyter_resource_usage/config.py

@@ -122,3 +122,10 @@ def _mem_limit_default(self):
     @default("cpu_limit")
     def _cpu_limit_default(self):
         return float(os.environ.get("CPU_LIMIT", 0))
+
+    enable_prometheus_metrics = Bool(
+        default_value=True,
+        help="""
+        Set to False in order to disable reporting of Prometheus style metrics.
+        """,
+    ).tag(config=True)

jupyter_resource_usage/server_extension.py

@@ -19,7 +19,12 @@ def load_jupyter_server_extension(server_app):
         ".*", [(url_path_join(base_url, "/api/metrics/v1"), ApiHandler)]
     )
 
-    callback = ioloop.PeriodicCallback(
-        PrometheusHandler(PSUtilMetricsLoader(server_app)), 1000
-    )
-    callback.start()
+    if resuseconfig.enable_prometheus_metrics:
+        callback = ioloop.PeriodicCallback(
+            PrometheusHandler(PSUtilMetricsLoader(server_app)), 1000
+        )
+        callback.start()
+    else:
+        server_app.log.info(
+            "Prometheus metrics reporting disabled in jupyter_resource_usage."
+        )