Add prometheus metric with version information (#1467)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: yuvipanda

jupyter_server/prometheus/metrics.py

@@ -5,19 +5,35 @@
 conventions for metrics & labels.
 """
 
+from prometheus_client import Gauge, Histogram, Info
+
+from jupyter_server._version import version_info as server_version_info
+
 try:
-    # Jupyter Notebook also defines these metrics.  Re-defining them results in a ValueError.
-    # Try to de-duplicate by using the ones in Notebook if available.
+    from notebook._version import version_info as notebook_version_info
+except ImportError:
+    notebook_version_info = None
+
+
+if (
+    notebook_version_info is not None  # No notebook package found
+    and notebook_version_info < (7,)  # Notebook package found, is version 6
+    # Notebook package found, but its version is the same as jupyter_server
+    # version. This means some package (looking at you, nbclassic) has shimmed
+    # the notebook package to instead be imports from the jupyter_server package.
+    # In such cases, notebook.prometheus.metrics is actually *this file*, so
+    # trying to import it will cause a circular import. So we don't.
+    and notebook_version_info != server_version_info
+):
+    # Jupyter Notebook v6 also defined these metrics.  Re-defining them results in a ValueError,
+    # so we simply re-export them if we are co-existing with the notebook v6 package.
     # See https://github.com/jupyter/jupyter_server/issues/209
     from notebook.prometheus.metrics import (
         HTTP_REQUEST_DURATION_SECONDS,
         KERNEL_CURRENTLY_RUNNING_TOTAL,
         TERMINAL_CURRENTLY_RUNNING_TOTAL,
     )
-
-except ImportError:
-    from prometheus_client import Gauge, Histogram
-
+else:
     HTTP_REQUEST_DURATION_SECONDS = Histogram(
         "http_request_duration_seconds",
         "duration in seconds for all HTTP requests",
@@ -35,9 +51,12 @@
         ["type"],
     )
 
+# New prometheus metrics that do not exist in notebook v6 go here
+SERVER_INFO = Info("jupyter_server", "Jupyter Server Version information")
 
 __all__ = [
     "HTTP_REQUEST_DURATION_SECONDS",
     "TERMINAL_CURRENTLY_RUNNING_TOTAL",
     "KERNEL_CURRENTLY_RUNNING_TOTAL",
+    "SERVER_INFO",
 ]

jupyter_server/serverapp.py

@@ -110,6 +110,7 @@
     GatewaySessionManager,
 )
 from jupyter_server.log import log_request
+from jupyter_server.prometheus.metrics import SERVER_INFO
 from jupyter_server.services.config import ConfigManager
 from jupyter_server.services.contents.filemanager import (
     AsyncFileContentsManager,
@@ -2696,6 +2697,12 @@ def _init_asyncio_patch() -> None:
                     # prefer Selector to Proactor for tornado + pyzmq
                     asyncio.set_event_loop_policy(WindowsSelectorEventLoopPolicy())
 
+    def init_metrics(self) -> None:
+        """
+        Initialize any prometheus metrics that need to be set up on server startup
+        """
+        SERVER_INFO.info({"version": __version__})
+
     @catch_config_error
     def initialize(
         self,
@@ -2763,6 +2770,7 @@ def initialize(
         self.load_server_extensions()
         self.init_mime_overrides()
         self.init_shutdown_no_activity()
+        self.init_metrics()
         if new_httpserver:
             self.init_httpserver()