Add jinja template support to pod-name config via environment variable (

#1368)

docs/source/users/kernel-envs.md

@@ -75,7 +75,10 @@ There are several supported `KERNEL_` variables that the Enterprise Gateway serv
     cases, Enterprise Gateway will honor that value.  However, when provided,
     it is the user's responsibility that KERNEL_POD_NAME is unique relative to
     any pods in the target namespace.  In addition, the pod must NOT exist -
-    unlike the case if KERNEL_NAMESPACE is provided.
+    unlike the case if KERNEL_NAMESPACE is provided. The KERNEL_POD_NAME can
+    also be provided as a jinja2 template string
+    (e.g "{{ kernel_prefix }}-{{ kernel_id | replace('-', '') }}")
+    which will be evaluated against existing list of environment variables.
 
   KERNEL_REMOTE_HOST=<remote host name>
     DistributedProcessProxy only.  When specified, this value will override the

enterprise_gateway/services/processproxies/k8s.py

@@ -10,6 +10,7 @@
 from typing import Any
 
 import urllib3
+from jinja2 import BaseLoader, Environment
 from kubernetes import client, config
 
 from ..kernels.remotemanager import RemoteKernelManager
@@ -216,8 +217,22 @@ def terminate_container_resources(self) -> bool | None:
 
     def _determine_kernel_pod_name(self, **kwargs: dict[str, Any] | None) -> str:
         pod_name = kwargs["env"].get("KERNEL_POD_NAME")
+
         if pod_name is None:
             pod_name = KernelSessionManager.get_kernel_username(**kwargs) + "-" + self.kernel_id
+        else:
+            self.log.debug(f"Processing KERNEL_POD_NAME based on env var => {pod_name}")
+            if "{{" in pod_name and "}}" in pod_name:
+                self.log.debug("Processing KERNEL_POD_NAME as jinja template")
+                # Create Jinja2 environment
+                keywords = {}
+                for name, value in kwargs["env"].items():
+                    if name.startswith("KERNEL_"):
+                        keywords[name.lower()] = value
+                keywords["kernel_id"] = self.kernel_id
+                self.log.debug("Processing pod_name jinja template")
+                env = Environment(loader=BaseLoader(), autoescape=True)
+                pod_name = env.from_string(pod_name).render(**keywords)
 
         # Rewrite pod_name to be compatible with DNS name convention
         # And put back into env since kernel needs this