feat: make it easier to reason about health check failures

Whenever a health check times out now, the most recently collected
error for each resource (if any) will be printed as part of the error
message. This excludes errors for those resources for which no error
was reported in the last update. This is because whenever a timeout
occurs, an error is reported on ALL resources, even those that have
been seen as healthy before.

Signed-off-by: Max Jonas Werner <mail@makk.es>

controllers/kustomization_healthcheck.go

@@ -59,10 +59,14 @@ func (hc *KustomizeHealthCheck) Assess(pollInterval time.Duration) error {
 	opts := polling.Options{PollInterval: pollInterval, UseCache: true}
 	eventsChan := hc.statusPoller.Poll(ctx, objMetadata, opts)
 	coll := collector.NewResourceStatusCollector(objMetadata)
+	lastStatus := make(map[object.ObjMetadata]*event.ResourceStatus)
 	done := coll.ListenWithObserver(eventsChan, collector.ObserverFunc(
 		func(statusCollector *collector.ResourceStatusCollector, e event.Event) {
 			var rss []*event.ResourceStatus
 			for _, rs := range statusCollector.ResourceStatuses {
+				if rs.Error == nil {
+					lastStatus[rs.Identifier] = rs
+				}
 				rss = append(rss, rs)
 			}
 			desired := status.CurrentStatus
@@ -81,14 +85,19 @@ func (hc *KustomizeHealthCheck) Assess(pollInterval time.Duration) error {
 	}
 
 	if ctx.Err() == context.DeadlineExceeded {
-		ids := []string{}
+		errors := []string{}
 		for _, rs := range coll.ResourceStatuses {
-			if rs.Status != status.CurrentStatus {
+			if lastStatus[rs.Identifier].Status != status.CurrentStatus {
 				id := hc.objMetadataToString(rs.Identifier)
-				ids = append(ids, id)
+				var bld strings.Builder
+				bld.WriteString(fmt.Sprintf("%s (status '%s')", id, lastStatus[rs.Identifier].Status))
+				if rs.Error != nil {
+					bld.WriteString(fmt.Sprintf(": %s", rs.Error))
+				}
+				errors = append(errors, bld.String())
 			}
 		}
-		return fmt.Errorf("Health check timed out for [%v]", strings.Join(ids, ", "))
+		return fmt.Errorf("Health check failed for [%s]", strings.Join(errors, ", "))
 	}
 
 	return nil