added healthy check in main.go

added healthy check in main.go
extended the ping check that creates a /tmp/healthy file if ping successfull and removes that file if ping failes 3 times.

With this you can add the following to the newt docker compose to do the health check:
healthcheck:
  test: ["CMD-SHELL", "test -f /tmp/healthy"]
  interval: 30s
  timeout: 10s
  retries: 3

main.go

@@ -127,7 +127,7 @@ func startPingCheck(tnet *netstack.Net, serverIP string, stopChan chan struct{})
 	go func() {
 		for {
 			select {
-				case <-ticker.C:
+			case <-ticker.C:
 				err := ping(tnet, serverIP)
 				if err != nil {
 					consecutiveFailures++
@@ -137,8 +137,9 @@ func startPingCheck(tnet *netstack.Net, serverIP string, stopChan chan struct{})
 					if consecutiveFailures >= 3 {
 						_ = os.Remove("/tmp/healthy")
 					}
-					// increase interval if it keeps failing
+					// Increase interval if we have consistent failures, with a maximum cap
 					if consecutiveFailures >= 3 && currentInterval < maxInterval {
+						// Increase by 50% each time, up to the maximum
 						currentInterval = time.Duration(float64(currentInterval) * 1.5)
 						if currentInterval > maxInterval {
 							currentInterval = maxInterval
@@ -152,7 +153,7 @@ func startPingCheck(tnet *netstack.Net, serverIP string, stopChan chan struct{})
 					if err != nil {
 						logger.Warn("Failed to write health file: %v", err)
 					}
-					// Reset interval if we increased it
+					// On success, if we've backed off, gradually return to normal interval
 					if currentInterval > initialInterval {
 						currentInterval = time.Duration(float64(currentInterval) * 0.8)
 						if currentInterval < initialInterval {
@@ -163,9 +164,9 @@ func startPingCheck(tnet *netstack.Net, serverIP string, stopChan chan struct{})
 					}
 					consecutiveFailures = 0
 				}
-				case <-stopChan:
+			case <-stopChan:
 				logger.Info("Stopping ping check")
-				return
+			return
 			}			
 		}
 	}()