Add configurable startup command (#18)

* adding configurable startup command

* adding configurable startup command

* adding configurable startup command

* addressing comments

* addressing comments

config.yaml

@@ -19,3 +19,7 @@ options:
     type: int
     description: "External port for Ingress configuration."
     default: 8080
+  startup_command:
+    type: string
+    description: Command required to start up the docker image provided.
+    default: "/srv/gunicorn/run"

src/charm.py

@@ -102,7 +102,7 @@ def _get_gunicorn_pebble_config(self, event: ops.framework.EventBase) -> dict:
                 "gunicorn": {
                     "override": "replace",
                     "summary": "gunicorn service",
-                    "command": "/srv/gunicorn/run",
+                    "command": self.config["startup_command"],
                     "startup": "enabled",
                 }
             },
@@ -202,7 +202,14 @@ def _configure_workload(self, event: ops.charm.EventBase) -> None:
             "About to add_layer with pebble_config: %s", yaml.dump(gunicorn_pebble_config)
         )
         gunicorn_container.add_layer("gunicorn", gunicorn_pebble_config, combine=True)
-        gunicorn_container.pebble.replan_services()
+        try:
+            gunicorn_container.pebble.replan_services()
+        except ops.pebble.ChangeError:
+            self.unit.status = BlockedStatus(
+                "Charm's startup command may be wrong, please check the config"
+            )
+            return
+
         statsd_container.add_layer(
             "statsd-prometheus-exporter", statsd_pebble_config, combine=True
         )

tests/unit/test_charm.py

@@ -5,7 +5,8 @@
 import unittest
 from unittest.mock import MagicMock, patch
 
-from ops import testing
+from ops import pebble, testing
+from ops.model import BlockedStatus
 from scenario import (
     JUJU_DEFAULT_CONFIG,
     TEST_JUJU_CONFIG,
@@ -416,6 +417,18 @@ def test_configure_workload_pebble_not_ready(self):
                 self.assertEqual(r, expected_ret)
             self.assertTrue(expected_output in logger.output[0])
 
+    def test_configure_workload_exception(self):
+
+        mock_event = MagicMock()
+
+        with patch("ops.model.Container.pebble", return_value=MagicMock()) as pebble_mock:
+            pebble_mock.replan_services.side_effect = pebble.ChangeError("abc", "def")
+            self.harness.charm._configure_workload(mock_event)
+            self.assertEqual(
+                self.harness.model.unit.status,
+                BlockedStatus("Charm's startup command may be wrong, please check the config"),
+            )
+
 
 if __name__ == "__main__":
     unittest.main()