WebSocket connection to 'ws://localhost:9001/mqtt' failed:
Error in connection establishment: net::ERR_CONNECTION_REFUSED

listener 9001
protocol websocket
http_dir /path_to_web_dir # not entirely sure if this line is necessary

> firewall-cmd --zone=public --permanent --add-port=9001/tcp
> firewall-cmd --reload

1556009330: mosquitto version 1.6.0 starting
1556009330: Config loaded from mosquitto.conf.
1556009330: Opening websockets listen socket on port 9001.
1556009330: Opening ipv4 listen socket on port 8883.
1556009330: Opening ipv6 listen socket on port 8883.