add loki connection check

service/forwarder.go

@@ -54,6 +54,28 @@ func ParseLokiUrl(params string) (*LokiConnection, error) {
 	}, nil
 }
 
+func (this *LokiConnection) Ready() error {
+
+	req, err := http.NewRequest("GET", this.url+"/ready", nil)
+	if err != nil {
+		return err
+	}
+
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		return err
+	}
+
+	defer resp.Body.Close()
+
+	switch resp.StatusCode {
+	case http.StatusOK, http.StatusAccepted, http.StatusNoContent:
+		return nil
+	}
+
+	return fmt.Errorf("http status code %d", resp.StatusCode)
+}
+
 type Level string
 
 func (lvl Level) String() string {

service/main.go

@@ -27,7 +27,6 @@ import (
 var migrationsFs embed.FS
 
 //	todo: add management API
-//	todo: pull txid out of timescale metadata
 
 func main() {
 
@@ -70,7 +69,15 @@ func main() {
 	}
 
 	if lokiConn != nil {
+
+		if err := lokiConn.Ready(); err != nil {
+			slog.Error("STARTUP: Loki is not ready",
+				slog.String("err", err.Error()))
+			os.Exit(1)
+		}
+
 		slog.Info("STARTUP: Loki connection OK")
+
 	} else {
 		slog.Info("STARTUP: Loki not configured. Using Timescale/Postgres")
 	}