k8s_exec: Select first container from the pod

kubectl command select first container from the pod in order
to execute commands on. We replicate the same behavior in k8s_exec
module.

Fixes: ansible-collections#358

Signed-off-by: Abhijeet Kasurde <[email protected]>

changelogs/fragments/358-k8s_exec.yml

@@ -0,0 +1,3 @@
+---
+minor_changes:
+- k8s_exec - select first container from the pod if none specified (https://github.com/ansible-collections/kubernetes.core/issues/358).

molecule/default/tasks/exec.yml

@@ -13,6 +13,21 @@
           - name: sleeper
             image: busybox
             command: ["sleep", "infinity"]
+    multi_container_pod_name: pod-2
+    multi_container_pod_definition:
+      apiVersion: v1
+      kind: Pod
+      metadata:
+        name: "{{ multi_container_pod_name }}"
+        namespace: "{{ exec_namespace }}"
+      spec:
+        containers:
+          - name: sleeper-1
+            image: busybox
+            command: ["sleep", "infinity"]
+          - name: sleeper-2
+            image: busybox
+            command: ["sleep", "infinity"]
 
   block:
     - name: "Ensure that {{ exec_namespace }} namespace exists"
@@ -57,6 +72,25 @@
           - command_status.rc != 0
           - command_status.return_code != 0
 
+    - name: Create a multi container pod
+      k8s:
+        definition: "{{ multi_container_pod_definition }}"
+        wait: yes
+        wait_sleep: 1
+        wait_timeout: 30
+
+    - name: Execute command on the first container of the pod
+      k8s_exec:
+        pod: "{{ multi_container_pod_name }}"
+        namespace: "{{ exec_namespace }}"
+        command: echo hello
+      register: output
+
+    - name: Assert k8s_exec output is correct
+      assert:
+        that:
+          - "'hello' in output.stdout"
+
   always:
     - name: "Cleanup namespace"
       k8s:

plugins/modules/k8s_exec.py

@@ -40,27 +40,28 @@
     description:
     - The URL of an HTTP proxy to use for the connection.
     - Can also be specified via I(K8S_AUTH_PROXY) environment variable.
-    - Please note that this module does not pick up typical proxy settings from the environment (e.g. HTTP_PROXY).
+    - Please note that this module does not pick up typical proxy settings from the environment (for example, HTTP_PROXY).
     type: str
   namespace:
     description:
-    - The pod namespace name
+    - The pod namespace name.
     type: str
     required: yes
   pod:
     description:
-    - The pod name
+    - The pod name.
     type: str
     required: yes
   container:
     description:
     - The name of the container in the pod to connect to.
     - Defaults to only container if there is only one container in the pod.
+    - If not specified, will choose the first container from the given pod as kubectl cmdline does.
     type: str
     required: no
   command:
     description:
-    - The command to execute
+    - The command to execute.
     type: str
     required: yes
 """
@@ -84,6 +85,13 @@
   debug:
     msg: "cmd failed"
   when: command_status.rc != 0
+
+- name: Specify a container name to execute the command on
+  kubernetes.core.k8s_exec:
+    namespace: myproject
+    pod: busybox-test
+    container: manager
+    command: echo "hello"
 """
 
 RETURN = r"""
@@ -134,6 +142,7 @@
 try:
     from kubernetes.client.apis import core_v1_api
     from kubernetes.stream import stream
+    from kubernetes.client.rest import ApiException
 except ImportError:
     # ImportError are managed by the common module already.
     pass
@@ -157,6 +166,19 @@ def execute_module(module, k8s_ansible_mixin):
     optional_kwargs = {}
     if module.params.get("container"):
         optional_kwargs["container"] = module.params["container"]
+    else:
+        # default to the first container available on pod
+        resp = None
+        try:
+            resp = api.read_namespaced_pod(
+                name=module.params["pod"], namespace=module.params["namespace"]
+            )
+        except ApiException:
+            pass
+
+        if resp and len(resp.spec.containers) >= 1:
+            optional_kwargs["container"] = resp.spec.containers[0].name
+
     try:
         resp = stream(
             api.connect_get_namespaced_pod_exec,