fix(updater): retain two verified backup generations

scripts/update/tests/host_storage_integration.py

@@ -1,5 +1,5 @@
 #!/usr/bin/env python3
-"""Real migration -> adoption -> two updates, including a backup restore, on synthetic data.
+"""Real migration -> adoption -> three updates, retention and restore on synthetic data.
 
 Requires local storage test images and registry:2; never contacts a FEDEO instance.
 Release HTTP/health responses are fixtures; Compose, registry, SDK, PostgreSQL,
@@ -101,7 +101,8 @@ def run():
             docker('push', image['repository'] + ':fixture')
         # Copy health, networking and SDK settings from the original fixture, but start the new image's migration script.
         updater.releases = Releases(config, images)
-        for version in ('3.4.0', '3.5.0'):
+        backups = []
+        for version in ('3.4.0', '3.5.0', '3.6.0'):
             http.version = version
             checked = updater.execute('check', version)
             assert checked['plan']['storageProvider'] == 'seaweedfs'
@@ -112,6 +113,15 @@ def run():
             old_matrix = migration.inspect(retained)
             assert not old_matrix['State']['Running'] and old_matrix['HostConfig']['RestartPolicy']['Name'] == 'no'
             backup = Path(result['backup'])
+            backups.append(backup)
+            retention = result['backupRetention']
+            assert retention['status'] == 'complete', retention
+            assert len(retention['retained']) == min(len(backups), 2)
+            if len(backups) == 3:
+                assert not backups[0].exists()
+                assert u.read_json(backups[0].parent / 'backup-pruned.json')['status'] == 'removed'
+                assert backups[1].is_dir() and backups[2].is_dir()
+                assert (root / '.updates/storage-migration/backup/complete.json').is_file()
             with tarfile.open(backup / 'files.tar') as archive:
                 assert archive.extractfile('matrix/postgres/retained.txt').read() == b'retired Matrix'
                 assert 'storage/config/s3.json' in archive.getnames()
@@ -136,7 +146,8 @@ def run():
             migration.helper('restore-verify', endpoint='http://' + restore_name + ':9000')
         finally:
             docker('rm', '-f', restore_name)
-        print(json.dumps({'result': 'passed', 'restoredUpdaterBackup': str(backup), 'evidence': str(root)}), flush=True)
+        print(json.dumps({'result': 'passed', 'retention': 'two_generations_verified',
+                          'restoredUpdaterBackup': str(backup), 'evidence': str(root)}), flush=True)
     except BaseException:
         print('Failure evidence: ' + str(root), flush=True)
         for path in sorted((root / '.updates').glob('*/commands.log')):