add ability to filter the list of pods to be drained by a pod label selector (#606)

* add ability to filter the list of pods to be drained by a label selector

plugins/modules/k8s_drain.py

@@ -41,6 +41,15 @@ options:
       - The name of the node.
     required: true
     type: str
+  pod_selectors:
+    description:
+      - Label selector to filter pods on the node.
+      - This option has effect only when C(state) is set to I(drain).
+    type: list
+    elements: str
+    version_added: 2.5.0
+    aliases:
+    - label_selectors
   delete_options:
     type: dict
     default: {}
@@ -116,6 +125,14 @@ EXAMPLES = r"""
     state: cordon
     name: foo
 
+- name: Drain node "foo" using label selector to filter the list of pods to be drained.
+  kubernetes.core.k8s_drain:
+    state: drain
+    name: foo
+    pod_selectors:
+    - 'app!=csi-attacher'
+    - 'app!=csi-provisioner'
+
 """
 
 RETURN = r"""
@@ -329,6 +346,17 @@ class K8sDrainAnsible(object):
                     )
                 )
 
+    def list_pods(self):
+        params = {
+            "field_selector": "spec.nodeName={name}".format(
+                name=self._module.params.get("name")
+            )
+        }
+        pod_selectors = self._module.params.get("pod_selectors")
+        if pod_selectors:
+            params["label_selector"] = ",".join(pod_selectors)
+        return self._api_instance.list_pod_for_all_namespaces(**params)
+
     def delete_or_evict_pods(self, node_unschedulable):
         # Mark node as unschedulable
         result = []
@@ -351,12 +379,7 @@ class K8sDrainAnsible(object):
                 self.patch_node(unschedulable=False)
 
         try:
-            field_selector = "spec.nodeName={name}".format(
-                name=self._module.params.get("name")
-            )
-            pod_list = self._api_instance.list_pod_for_all_namespaces(
-                field_selector=field_selector
-            )
+            pod_list = self.list_pods()
             # Filter pods
             force = self._drain_options.get("force", False)
             ignore_daemonset = self._drain_options.get("ignore_daemonsets", False)
@@ -487,6 +510,11 @@ def argspec():
                     wait_sleep=dict(type="int", default=5),
                 ),
             ),
+            pod_selectors=dict(
+                type="list",
+                elements="str",
+                aliases=["label_selectors"],
+            ),
         )
     )
     return argument_spec