code: func convertExtraHosts(extraHosts composetypes.HostsList) []string {
  	hosts := []string{}
  	for _, hostIP := range extraHosts {
  		if v := strings.SplitN(hostIP, ":", 2); len(v) == 2 {
  			// Convert to SwarmKit notation: IP-address hostname(s)
  			hosts = append(hosts, fmt.Sprintf("%s %s", v[1], v[0]))
  		}
  	}
  	return hosts
  }
docs: // convertExtraHosts converts <host>:<ip> mappings to SwarmKit notation:
  // "IP-address hostname(s)". The original order of mappings is preserved.