[BGS-144] Introspection watcher should notify when subgraph hosts change connection status.

Author: monkpow

src/composition/supergraph/config/error/subgraph.rs

@@ -26,7 +26,7 @@ pub enum ResolveSubgraphError {
     #[error(transparent)]
     Fs(Box<dyn std::error::Error + Send + Sync>),
     /// Occurs when a introspection against a subgraph fails
-    #[error("Failed to introspect the subgraph {subgraph_name}.")]
+    #[error("Failed to introspect the subgraph \"{subgraph_name}\".")]
     IntrospectionError {
         /// The subgraph name that failed to be resolved
         subgraph_name: String,

src/composition/watchers/subgraphs.rs

@@ -170,7 +170,7 @@ impl SubtaskHandleStream for SubgraphWatchers {
                 match diff {
                     Ok(diff) => {
                         // If we detect additional diffs, start a new subgraph subtask.
-                        // Adding the abort handle to the currentl collection of handles.
+                        // Adding the abort handle to the current collection of handles.
                         for (subgraph_name, subgraph_config) in diff.added() {
                             let _ = subgraph_handles.add(
                                 subgraph_name,

src/composition/watchers/watcher/introspection.rs

@@ -50,8 +50,17 @@ impl SubgraphIntrospection {
             .skip(1)
             .filter_map(|change| async move {
                 match change {
-                    Ok(subgraph) => Some(subgraph),
+                    Ok(subgraph) => {
+                        eprintln!(
+                            "Connectivity restored for subgraph \"{}\".\n",
+                            subgraph.name()
+                        );
+                        Some(subgraph)
+                    }
                     Err(err) => {
+                        eprintln!("Error detected communicating with subgraph: {}", err);
+                        eprintln!("Note: Schema changes will not be reflected.");
+                        eprintln!("Will retry but subgraph logs should be inspected.\n\n");
                         tracing::error!("{:?}", err);
                         None
                     }