fix: don't mount cache directories in lxd base instances (#473)

craft_providers/base.py

@@ -979,6 +979,7 @@ def setup(
         *,
         executor: Executor,
         timeout: Optional[float] = TIMEOUT_UNPREDICTABLE,
+        mount_cache: bool = True,
     ) -> None:
         """Prepare base instance for use by the application.
 
@@ -994,6 +995,7 @@ def setup(
 
         :param executor: Executor for target container.
         :param timeout: Timeout in seconds.
+        :param mount_cache: If true, mount the cache directories.
 
         :raises BaseCompatibilityError: if instance is incompatible.
         :raises BaseConfigurationError: on other unexpected error.
@@ -1015,7 +1017,8 @@ def setup(
 
         self._update_compatibility_tag(executor=executor)
 
-        self._mount_shared_cache_dirs(executor=executor)
+        if mount_cache:
+            self._mount_shared_cache_dirs(executor=executor)
 
         self._pre_setup_os(executor=executor)
         self._setup_os(executor=executor)

craft_providers/lxd/launcher.py

@@ -143,7 +143,10 @@ def _create_instance(
             )
             config_timer = InstanceTimer(base_instance)
             config_timer.start()
-            base_configuration.setup(executor=base_instance)
+
+            # The base configuration shouldn't mount cache directories because if
+            # they get deleted, copying the base instance will fail.
+            base_configuration.setup(executor=base_instance, mount_cache=False)
             _set_timezone(
                 base_instance,
                 base_instance.project,
@@ -219,7 +222,10 @@ def _create_instance(
         instance.restart()
     else:
         instance.start()
-    base_configuration.wait_until_ready(executor=instance)
+    # Warmup the instance to ensure we have everything set up.
+    # There are cases where setup won't do everything to the base instance that
+    # warmup does to the final instance (such as mounting cache directories).
+    base_configuration.warmup(executor=instance)
 
 
 def _ensure_project_exists(

tests/integration/lxd/test_launcher.py

@@ -55,11 +55,12 @@ def _base_instance(
 
 
 @pytest.fixture()
-def base_configuration():
+def base_configuration(tmp_path):
     """Returns a simple base configuration."""
     return ubuntu.BuilddBase(
         alias=ubuntu.BuilddBaseAlias.JAMMY,
         hostname="test-hostname",
+        cache_path=tmp_path / "cache",
     )
 
 
@@ -224,6 +225,10 @@ def test_launch_use_base_instance(
     # fingerprint the base instance
     base_instance.start()
     base_instance.execute_run(["touch", "/base-instance"])
+    assert (
+        base_instance.execute_run(["ls", "/root/.cache/pip/"], check=False).returncode
+        == 2
+    )
     base_instance.stop()
 
     # delete the instance so a new instance is created from the base instance
@@ -270,6 +275,8 @@ def test_launch_use_base_instance(
 
     assert instance_hostname == instance.instance_name
 
+    instance.execute_run(["ls", "/root/.cache/pip/"], check=True)
+
 
 def test_launch_create_base_instance_with_correct_image_description(
     base_configuration, get_base_instance, instance_name

tests/unit/lxd/test_launcher.py

@@ -182,7 +182,7 @@ def test_launch_no_base_instance(
     assert mock_base_configuration.mock_calls == [
         call.get_command_environment(),
         call.setup(executor=fake_instance),
-        call.wait_until_ready(executor=fake_instance),
+        call.warmup(executor=fake_instance),
     ]
 
 
@@ -247,8 +247,8 @@ def test_launch_use_base_instance(
     assert mock_base_configuration.mock_calls == [
         call.get_command_environment(),
         call.get_command_environment(),
-        call.setup(executor=fake_base_instance),
-        call.wait_until_ready(executor=fake_instance),
+        call.setup(executor=fake_base_instance, mount_cache=False),
+        call.warmup(executor=fake_instance),
     ]
 
 
@@ -527,8 +527,8 @@ def test_launch_existing_base_instance_invalid(
     assert mock_base_configuration.mock_calls == [
         call.get_command_environment(),
         call.get_command_environment(),
-        call.setup(executor=fake_base_instance),
-        call.wait_until_ready(executor=fake_instance),
+        call.setup(executor=fake_base_instance, mount_cache=False),
+        call.warmup(executor=fake_instance),
     ]
 
 
@@ -609,7 +609,7 @@ def test_launch_all_opts(
     assert mock_base_configuration.mock_calls == [
         call.get_command_environment(),
         call.setup(executor=fake_instance),
-        call.wait_until_ready(executor=fake_instance),
+        call.warmup(executor=fake_instance),
     ]
 
 
@@ -703,7 +703,7 @@ def test_launch_create_project(
     assert mock_base_configuration.mock_calls == [
         call.get_command_environment(),
         call.setup(executor=fake_instance),
-        call.wait_until_ready(executor=fake_instance),
+        call.warmup(executor=fake_instance),
     ]
 
 
@@ -846,7 +846,7 @@ def test_launch_with_existing_instance_incompatible_with_auto_clean(
         call.get_command_environment(),
         call.warmup(executor=fake_instance),
         call.setup(executor=fake_instance),
-        call.wait_until_ready(executor=fake_instance),
+        call.warmup(executor=fake_instance),
     ]
 
 
@@ -940,7 +940,7 @@ def test_launch_with_existing_ephemeral_instance(
     assert mock_base_configuration.mock_calls == [
         call.get_command_environment(),
         call.setup(executor=fake_instance),
-        call.wait_until_ready(executor=fake_instance),
+        call.warmup(executor=fake_instance),
     ]
 
 
@@ -1133,8 +1133,8 @@ def test_use_snapshots_deprecated(
     assert mock_base_configuration.mock_calls == [
         call.get_command_environment(),
         call.get_command_environment(),
-        call.setup(executor=fake_base_instance),
-        call.wait_until_ready(executor=fake_instance),
+        call.setup(executor=fake_base_instance, mount_cache=False),
+        call.warmup(executor=fake_instance),
     ]