Ensure kernel modules are loaded after reboot (#122)

src/charm.py

@@ -679,6 +679,13 @@ def _install_repo_policy_compliance(self) -> bool:
         )
         return old_version != new_version
 
+    def _enable_kernel_modules(self) -> None:
+        """Enable kernel modules needed by the charm."""
+        execute_command(["/usr/sbin/modprobe", "br_netfilter"])
+
+        with open("/etc/modules", "a", encoding="utf-8") as modules_file:
+            modules_file.write("br_netfilter\n")
+
     @retry(tries=10, delay=15, max_delay=60, backoff=1.5, local_logger=logger)
     def _install_deps(self) -> None:
         """Install dependencies."""
@@ -710,7 +717,7 @@ def _install_deps(self) -> None:
         execute_command(["/snap/bin/lxc", "network", "set", "lxdbr0", "ipv6.address", "none"])
         execute_command(["/snap/bin/lxd", "waitready"])
         if not LXD_PROFILE_YAML.exists():
-            execute_command(["/usr/sbin/modprobe", "br_netfilter"])
+            self._enable_kernel_modules()
         execute_command(
             [
                 "/snap/bin/lxc",

tests/unit/test_charm.py

@@ -66,7 +66,8 @@ def test_proxy_setting(self):
 
     @patch("pathlib.Path.write_text")
     @patch("subprocess.run")
-    def test_install(self, run, wt):
+    @patch("builtins.open")
+    def test_install(self, open, run, wt):
         harness = Harness(GithubRunnerCharm)
         harness.begin()
         harness.charm.on.install.emit()
@@ -225,7 +226,8 @@ def test_get_runner_manager(self, run, wt, mkdir):
     @patch("pathlib.Path.mkdir")
     @patch("pathlib.Path.write_text")
     @patch("subprocess.run")
-    def test_on_install_failure(self, run, wt, mkdir, rm):
+    @patch("builtins.open")
+    def test_on_install_failure(self, open, run, wt, mkdir, rm):
         """Test various error thrown during install."""
 
         rm.return_value = mock_rm = MagicMock()