wip: fix up logging after instance put failures; add TODO

nexus/src/app/instance.rs

@@ -1109,6 +1109,13 @@ impl super::Nexus {
                     // Internal server error (or anything else) should change
                     // the instance state to failed, we don't know what state
                     // the instance is in.
+                    //
+                    // TODO(gjc) do we also need to clear the propolis_id at
+                    // this point? this is a tricky bit in start saga unwind: we
+                    // want to set the instance back to Stopped, but this
+                    // failure can move the instance to Failed without actually
+                    // clearing the active Propolis ID, which prevents it from
+                    // being deleted. hmm.
                     _ => {
                         let new_instance = db::model::InstanceVmmState {
                             no_vmm_state: db::model::InstanceState::new(
@@ -1121,6 +1128,11 @@ impl super::Nexus {
                             ..prev_instance_vmm.clone()
                         };
 
+                        info!(self.log,
+                              "setting instance to Failed after failed state change";
+                              "instance_id" => %instance_id,
+                              "new_state" => ?new_instance);
+
                         // XXX what if this fails?
                         let result = self
                             .db_datastore
@@ -1130,12 +1142,14 @@ impl super::Nexus {
                             )
                             .await;
 
-                        error!(
-                            self.log,
-                            "error setting Failed state after bad instance_put";
-                            "instance_id" => %instance_id,
-                            "result" => ?result
-                        );
+                        if result.is_err() {
+                            error!(
+                                self.log,
+                                "error setting Failed state after bad instance_put";
+                                "instance_id" => %instance_id,
+                                "result" => ?result
+                            );
+                        }
 
                         Err(e)
                     }