fix: handle None return from get_container_runtime()

The get_container_runtime() method was returning None when called
immediately after cluster creation, before any nodes reached Ready state.
This caused a TypeError: argument of type 'NoneType' is not iterable
when the code tried to check if 'docker' was in the runtime string.

Changes:
- Add retry logic with 60s timeout to get_container_runtime() to wait
  for at least one node to become Ready
- Add explicit None check in SymptomFaultInjector.__init__() with
  a clear error message if container runtime cannot be detected

Fixes network_delay, pod_failure, and other chaos mesh injection tasks
that were crashing on initialization.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: Rahuldrabit

aiopslab/generators/fault/inject_symp.py

@@ -28,6 +28,12 @@ def __init__(self, namespace: str):
 
         container_runtime = self.kubectl.get_container_runtime()
 
+        if container_runtime is None:
+            raise ValueError(
+                "Could not detect container runtime. "
+                "Ensure the cluster is running and at least one node is Ready."
+            )
+
         if "docker" in container_runtime:
             pass
         elif "containerd" in container_runtime:

aiopslab/service/kubectl.py

@@ -54,15 +54,27 @@ def get_cluster_ip(self, service_name, namespace):
         service_info = self.core_v1_api.read_namespaced_service(service_name, namespace)
         return service_info.spec.cluster_ip  # type: ignore
 
-    def get_container_runtime(self):
+    def get_container_runtime(self, max_wait: int = 60, poll_interval: int = 2):
         """
             Retrieve the container runtime used by the cluster.
             If the cluster uses multiple container runtimes, the first one found will be returned.
+            
+            Args:
+                max_wait: Maximum seconds to wait for a Ready node (default: 60)
+                poll_interval: Seconds between checks (default: 2)
+            
+            Returns:
+                Container runtime version string, or None if no Ready node found within max_wait.
         """
-        for node in self.core_v1_api.list_node().items:
-            for status in node.status.conditions:
-                if status.type == "Ready" and status.status == "True":
-                    return node.status.node_info.container_runtime_version
+        elapsed = 0
+        while elapsed < max_wait:
+            for node in self.core_v1_api.list_node().items:
+                for status in node.status.conditions:
+                    if status.type == "Ready" and status.status == "True":
+                        return node.status.node_info.container_runtime_version
+            time.sleep(poll_interval)
+            elapsed += poll_interval
+        return None
 
     def get_pod_name(self, namespace, label_selector):
         """Get the name of the first pod in a namespace that matches a given label selector."""