Log instance on initialization and when running a job (#1150)

* log instances

* add _default_instance & fix lint

* add test

* change var name to current_instance

qiskit_ibm_runtime/qiskit_runtime_service.py

@@ -219,6 +219,10 @@ def __init__(
                 for backend_name in hgp.backends:
                     if backend_name not in self._backends:
                         self._backends[backend_name] = None
+            self._current_instance = self._account.instance
+            if not self._current_instance:
+                self._current_instance = self._get_hgp().name
+                logger.info("Default instance: %s", self._current_instance)
         QiskitRuntimeService.global_service = self
 
         # TODO - it'd be nice to allow some kind of autocomplete, but `service.ibmq_foo`
@@ -988,6 +992,9 @@ def run(
             # Find the right hgp
             hgp = self._get_hgp(instance=qrt_options.instance, backend_name=qrt_options.backend)
             hgp_name = hgp.name
+            if hgp_name != self._current_instance:
+                self._current_instance = hgp_name
+                logger.info("Instance selected: %s", self._current_instance)
         backend = self.backend(name=qrt_options.backend, instance=hgp_name)
         status = backend.status()
         if status.operational is True and status.status_msg != "active":

releasenotes/notes/log-instance-selected-a18c4791418b5e0d.yaml

@@ -0,0 +1,7 @@
+---
+features:
+  - |
+    At initialization, if not passed in directly, the default ``instance`` selected by the provider 
+    will be logged at the "INFO" level. When running a job, if the backend selected is not in 
+    the default instance but in a different instance the user also has access to, that instance 
+    will also be logged. 

test/integration/test_account.py

@@ -80,3 +80,13 @@ def test_resolve_crn_for_invalid_service_instance_name(self):
                 token=self.dependencies.token,
                 instance=service_instance_name,
             )
+
+    def test_logging_instance_at_init(self):
+        """Test instance is logged at initialization if instance not passed in."""
+        with self.assertLogs("qiskit_ibm_runtime", "INFO") as logs:
+            QiskitRuntimeService(
+                channel="ibm_quantum",
+                url=self.dependencies.url,
+                token=self.dependencies.token,
+            )
+        self.assertIn("instance", logs.output[0])