Constructor provides a path to alternate optional kubectl

ops/charms/node_base.py

@@ -2,9 +2,10 @@
 
 import json
 import logging
-from subprocess import run
-from os import PathLike
 import time
+from os import PathLike
+from pathlib import Path
+from subprocess import run
 from typing import Union, List, Mapping, Optional, Protocol, Tuple
 
 from ops import Model, Object, CharmMeta, StoredState
@@ -35,10 +36,16 @@ class NodeLabelError(Exception):
 
         pass
 
-    def __init__(self, charm: Charm, kubeconfig_path: Union[PathLike, str]):
+    def __init__(
+        self,
+        charm: Charm,
+        kubeconfig_path: Union[PathLike, str],
+        kubectl: Optional[PathLike] = "/snap/bin/kubectl",
+    ):
         super().__init__(parent=charm, key="NodeBase")
-        self.kubeconfig_path = kubeconfig_path
         self.charm = charm
+        self.kubeconfig_path = kubeconfig_path
+        self.kubectl_path = kubectl
         self._stored.set_default(current_labels=dict())
 
     @staticmethod
@@ -56,13 +63,22 @@ def _retried_call(
         else:
             raise LabelMaker.NodeLabelError(retry_msg)
 
+    def _kubectl(self, command: str) -> str:
+        if not Path(self.kubectl_path).exists():
+            retry_msg = "Failed to find kubectl. Will retry."
+            stdout, _ = self._retried_call(["which", "kubectl"], retry_msg)
+            self.kubectl_path = stdout.decode().strip()
+
+        base = "{0} --kubeconfig={1}".format(self.kubectl_path, self.kubeconfig_path)
+        return base + " " + command
+
     def active_labels(self) -> Optional[Mapping[str, str]]:
         """
         Returns all existing labels if the api server can fetch from the node,
         otherwise returns None indicating the node cannot be relabeled.
         """
-        cmd = "kubectl --kubeconfig={0} get node {1} -o=jsonpath={{.metadata.labels}}"
-        cmd = cmd.format(self.kubeconfig_path, self.charm.get_node_name())
+        cmd = self._kubectl("get node {0} -o=jsonpath={{.metadata.labels}}")
+        cmd = cmd.format(self.charm.get_node_name())
         retry_msg = "Failed to get labels. Will retry."
         try:
             label_json, _ = LabelMaker._retried_call(cmd.split(), retry_msg)
@@ -82,8 +98,8 @@ def set_label(self, label: str, value: str) -> None:
         @param str value: Value to associate with the label
         @raises LabelMaker.NodeLabelError: if the label cannot be added
         """
-        cmd = "kubectl --kubeconfig={0} label node {1} {2}={3} --overwrite"
-        cmd = cmd.format(self.kubeconfig_path, self.charm.get_node_name(), label, value)
+        cmd = self._kubectl("label node {0} {1}={2} --overwrite")
+        cmd = cmd.format(self.charm.get_node_name(), label, value)
         retry_msg = "Failed to apply label {0}={1}. Will retry.".format(label, value)
         LabelMaker._retried_call(cmd.split(), retry_msg)
 
@@ -94,8 +110,8 @@ def remove_label(self, label: str) -> None:
         @param str label: Label name to remove
         @raises LabelMaker.NodeLabelError: if the label cannot be removed
         """
-        cmd = "kubectl --kubeconfig={0} label node {1} {2}-"
-        cmd = cmd.format(self.kubeconfig_path, self.charm.get_node_name(), label)
+        cmd = self._kubectl("label node {0} {1}-")
+        cmd = cmd.format(self.charm.get_node_name(), label)
         retry_msg = "Failed to remove label {0}. Will retry.".format(label)
         LabelMaker._retried_call(cmd.split(), retry_msg)
 

ops/tests/unit/test_ops.py

@@ -93,7 +93,7 @@ def test_active_labels_apply_layers_with_cloud(subprocess_run, harness):
         [
             mock.call(
                 [
-                    "kubectl",
+                    "/snap/bin/kubectl",
                     f"--kubeconfig={KUBE_CONFIG}",
                     "label",
                     "node",
@@ -123,7 +123,7 @@ def test_active_labels_apply_layers_from_config(subprocess_run, harness, caplog)
         [
             mock.call(
                 [
-                    "kubectl",
+                    "/snap/bin/kubectl",
                     f"--kubeconfig={KUBE_CONFIG}",
                     "label",
                     "node",