Enforce that provider run inside k8s cluster

Also set appropriate version dependencies.

Author: kevin-bates

kubernetes_kernel_provider/provider.py

@@ -1,9 +1,48 @@
 """Provides support for launching and managing kernels within a Kubernetes cluster."""
-
+import os
+from datetime import datetime
+from kubernetes import config
+from kubernetes.config.config_exception import ConfigException
 from remote_kernel_provider import RemoteKernelProviderBase
 
 
+LOGGED_WARNING_INTERVAL = int(os.getenv("K8SKP_LOGGED_WARNING_INTERVAL_SECS", "600"))  # log no more than every 10 min
+last_logged_warning = datetime.min
+first_time = True
+in_cluster = False
+
+
 class KubernetesKernelProvider(RemoteKernelProviderBase):
     id = 'k8skp'
     kernel_file = 'k8skp_kernel.json'
     lifecycle_manager_classes = ['kubernetes_kernel_provider.k8s.KubernetesKernelLifecycleManager']
+
+    def find_kernels(self):
+        """ Ensures the provider is running within a Kubernetes cluster.  If not, it will
+            log a warning message and no kernelspecs will be returned.  Since find_kernels()
+            is frequently called, it will only log the warning periodically (10 minutes by default).
+        """
+        global first_time, in_cluster, last_logged_warning
+
+        # Only check the cluster config once since the results can't change unless restarted.
+        if first_time:
+            try:
+                config.load_incluster_config()
+                in_cluster = True
+            except ConfigException as ce:
+                # Check to see if we're in-cluster via env.  If in-cluster, periodically
+                # log a warning
+                if os.getenv('KUBERNETES_SERVICE_HOST') is not None:
+                    raise ce  # Got an exception in-cluster - let it be known
+            first_time = False
+
+        if not in_cluster:
+            current_time = datetime.now()
+            delta = current_time - last_logged_warning
+            if delta.days > 0 or delta.seconds > LOGGED_WARNING_INTERVAL:
+                self.log.warning("KubernetesKernelProvider must be run from within a Kubernetes "
+                                 "cluster.  No Kubernetes kernels will be available.")
+                last_logged_warning = current_time
+            return {}
+
+        return super(KubernetesKernelProvider, self).find_kernels()

setup.py

@@ -61,10 +61,10 @@ def run(self):
         'Programming Language :: Python :: 3',
     ],
     install_requires = [
-        'remote_kernel_provider',
-        'jupyter_kernel_mgmt',
         'entrypoints',
-	    'kubernetes>=4.0.0',
+        'kubernetes>=4.0.0',
+        'jupyter_kernel_mgmt>=0.4.0',
+        'remote_kernel_provider>=0.2.0',
     ],
     extras_require   = {
         'test': ['mock', 'pytest'],