ability to working in produce only mode

Author: wolfy-j

config.go

@@ -40,7 +40,7 @@ func (c *Config) Hydrate(cfg service.Config) (err error) {
 		return err
 	}
 
-	if c.Workers.Pool != nil {
+	if c.Workers.Command != "" {
 		if err := c.Workers.Pool.Valid(); err != nil {
 			return c.Workers.Pool.Valid()
 		}

service.go

@@ -76,7 +76,7 @@ func (svc *Service) Init(
 	}
 
 	// limit the number of parallel threads
-	if svc.cfg.Workers.Pool != nil {
+	if svc.cfg.Workers.Command != "" {
 		svc.execPool = make(chan Handler, svc.cfg.Workers.Pool.NumWorkers)
 		for i := int64(0); i < svc.cfg.Workers.Pool.NumWorkers; i++ {
 			svc.execPool <- svc.exec