helm: use --rollback-on-failure for atomic on Helm v4 (#1144)

* helm: use --rollback-on-failure for atomic on Helm v4

Helm v4 renamed the `--atomic` flag to `--rollback-on-failure`. The old
flag is deprecated on `helm upgrade` and removed entirely from `helm
install`, so `atomic: true` failed against Helm v4 (issue #1143).

Emit the version-appropriate flag from deploy() using the existing
is_helm_v4() helper, covering both the upgrade and the replace/install
code paths. The public `atomic` option is unchanged.

Fixes: https://github.com/ansible-collections/kubernetes.core/issues/1143

Co-Authored-By: Claude Opus 4.8

* fix wrong link in the changelog fragment

Signed-off-by: Yuriy Novostavskiy <yuriy@novostavskiy.kyiv.ua>

---------

Signed-off-by: Yuriy Novostavskiy <yuriy@novostavskiy.kyiv.ua>

changelogs/fragments/20260611-helm-atomic-helm-v4.yml

@@ -0,0 +1,2 @@
+bugfixes:
+  - helm - use the ``--rollback-on-failure`` flag instead of the deprecated/removed ``--atomic`` flag when ``atomic=true`` is used with Helm v4 (https://github.com/ansible-collections/kubernetes.core/pull/1144).

plugins/modules/helm.py

@@ -202,6 +202,9 @@ options:
   atomic:
     description:
       - If set, the installation process deletes the installation on failure.
+      - With Helm v4 this is translated to the C(--rollback-on-failure) flag, since
+        C(--atomic) was renamed; with Helm v3 the C(--atomic) flag is used. The
+        O(atomic) option works the same way regardless of the installed Helm version.
     type: bool
     default: False
   server_side:
@@ -656,6 +659,12 @@ def deploy(
             deploy_command += " --timeout " + wait_timeout
 
     if atomic:
+        # Helm v4 renamed '--atomic' to '--rollback-on-failure'. The old flag is
+        # deprecated on 'helm upgrade' and removed from 'helm install', so always
+        # emit the version-appropriate flag.
+        if module.is_helm_v4():
+            deploy_command += " --rollback-on-failure"
+        else:
             deploy_command += " --atomic"
 
     if timeout:

tests/unit/modules/test_module_helm.py

@@ -710,3 +710,81 @@ class TestForceFlagHelmVersion(unittest.TestCase):
                 }
             )
             helm.main()
+
+
+class TestAtomicFlagHelmVersion(unittest.TestCase):
+    """Helm v4 renamed '--atomic' to '--rollback-on-failure' (issue #1143)."""
+
+    def setUp(self):
+        self.mock_module_helper = patch.multiple(
+            basic.AnsibleModule,
+            exit_json=exit_json,
+            fail_json=fail_json,
+            get_bin_path=get_bin_path,
+        )
+        self.mock_module_helper.start()
+        self.addCleanup(self.mock_module_helper.stop)
+
+        self.chart_info = {
+            "apiVersion": "v2",
+            "appVersion": "default",
+            "description": "A chart used in molecule tests",
+            "name": "test-chart",
+            "type": "application",
+            "version": "0.1.0",
+        }
+
+    def _run_with_version(self, args, helm_version):
+        set_module_args(args)
+        helm.get_release_status = MagicMock(return_value=None)
+        helm.fetch_chart_info = MagicMock(return_value=self.chart_info)
+        with patch.object(
+            helm.AnsibleHelmModule, "get_helm_version", return_value=helm_version
+        ):
+            with patch.object(basic.AnsibleModule, "run_command") as mock_run_command:
+                mock_run_command.return_value = (0, "configuration updated", "")
+                with self.assertRaises(AnsibleExitJson) as result:
+                    helm.main()
+        return result.exception.args[0]["command"]
+
+    def test_atomic_uses_atomic_flag_on_helm_v3(self):
+        command = self._run_with_version(
+            {
+                "release_name": "test",
+                "release_namespace": "test",
+                "chart_ref": "chart1",
+                "atomic": True,
+            },
+            "3.17.0",
+        )
+        assert "--atomic" in command
+        assert "--rollback-on-failure" not in command
+
+    def test_atomic_uses_rollback_on_failure_on_helm_v4(self):
+        command = self._run_with_version(
+            {
+                "release_name": "test",
+                "release_namespace": "test",
+                "chart_ref": "chart1",
+                "atomic": True,
+            },
+            "4.0.0",
+        )
+        assert "--rollback-on-failure" in command
+        assert "--atomic" not in command
+
+    def test_atomic_with_replace_uses_rollback_on_failure_on_helm_v4(self):
+        # 'replace' uses 'helm install', where '--atomic' is removed in v4.
+        command = self._run_with_version(
+            {
+                "release_name": "test",
+                "release_namespace": "test",
+                "chart_ref": "chart1",
+                "atomic": True,
+                "replace": True,
+            },
+            "4.0.0",
+        )
+        assert " install " in command
+        assert "--rollback-on-failure" in command
+        assert "--atomic" not in command