Tweak exec command for the topology observer

renovate.json

@@ -43,7 +43,7 @@
       "groupName": "Juju 2"
     }, {
       "matchPackageNames": ["urllib3"],
-      "allowedVersions": "<2.0.0"
+      "allowedVersions": "<2.1.0"
     }, {
       "matchPackageNames": ["pydantic"],
       "allowedVersions": "<2.0.0"

src/charm.py

@@ -99,7 +99,12 @@ def __init__(self, *args):
 
         self.secrets = {APP_SCOPE: {}, UNIT_SCOPE: {}}
 
-        self._observer = ClusterTopologyObserver(self)
+        juju_version = JujuVersion.from_environ()
+        if juju_version.major > 2:
+            run_cmd = "/usr/bin/juju-exec"
+        else:
+            run_cmd = "/usr/bin/juju-run"
+        self._observer = ClusterTopologyObserver(self, run_cmd)
         self.framework.observe(self.on.cluster_topology_change, self._on_cluster_topology_change)
         self.framework.observe(self.on.install, self._on_install)
         self.framework.observe(self.on.leader_elected, self._on_leader_elected)

src/cluster_topology_observer.py

@@ -42,15 +42,17 @@ class ClusterTopologyObserver(Object):
     Observed cluster topology changes cause :class"`ClusterTopologyChangeEvent` to be emitted.
     """
 
-    def __init__(self, charm: CharmBase):
+    def __init__(self, charm: CharmBase, run_cmd: str):
         """Constructor for ClusterTopologyObserver.
 
         Args:
             charm: the charm that is instantiating the library.
+            run_cmd: run command to use to dispatch events.
         """
         super().__init__(charm, "cluster-topology-observer")
 
         self._charm = charm
+        self._run_cmd = run_cmd
 
     def start_observer(self):
         """Start the cluster topology observer running in a new process."""
@@ -79,7 +81,7 @@ def start_observer(self):
                 "src/cluster_topology_observer.py",
                 self._charm._patroni._patroni_url,
                 f"{self._charm._patroni.verify}",
-                "/usr/bin/juju-run",
+                self._run_cmd,
                 self._charm.unit.name,
                 self._charm.charm_dir,
             ],

tests/unit/test_cluster_topology_observer.py

@@ -41,7 +41,7 @@ class MockCharm(CharmBase):
     def __init__(self, *args):
         super().__init__(*args)
 
-        self.observer = ClusterTopologyObserver(self)
+        self.observer = ClusterTopologyObserver(self, "test-command")
         self.framework.observe(self.on.cluster_topology_change, self._on_cluster_topology_change)
 
     def _on_cluster_topology_change(self, _) -> None: