set driver to unhealthy once if it cannot be detected in periodic check

client/fingerprint_manager.go

@@ -1,6 +1,7 @@
 package client
 
 import (
+	"fmt"
 	"log"
 	"strings"
 	"sync"
@@ -308,6 +309,19 @@ func (fm *FingerprintManager) watchDriver(d driver.Driver, name string) {
 				if err := fm.runDriverHealthCheck(name, hc); err != nil {
 					fm.logger.Printf("[DEBUG] client.fingerprint_manager: health checking for %v failed: %v", name, err)
 				}
+			} else {
+				// If the driver is undetected, change the health status to unhealthy
+				// only once.
+				healthInfo := &structs.DriverInfo{
+					Healthy:           false,
+					HealthDescription: fmt.Sprintf("Driver %s is not detected", name),
+					UpdateTime:        time.Now(),
+				}
+				if node := fm.updateNodeFromDriver(name, nil, healthInfo); node != nil {
+					fm.nodeLock.Lock()
+					fm.node = node
+					fm.nodeLock.Unlock()
+				}
 			}
 		}
 	}