Does kafka have any default web UI

1) No Kafka does not have a default UI.

There are however a number of third party tools that can graphically display Kafka resources. Just Google for kafka ui and pick the tool that displays what you want and you like the most.

2) To gracefully shutdown a Kafka broker, just send a SIGTERM to the Kafka process and it will properly shutdown. This can be done via the ./bin/kafka-server-stop.sh tool.

If it's part of a cluster, new leaders will be elected on other brokers, otherwise it will simply cleanly close all its resources. Note that depending on the number of partitions, this can take a few minutes.

You can try Landoop Kafka UI: https://github.com/Landoop/fast-data-dev They provide a nice Web-UI for Kafka topics, Avro schemata, Kafka Connect and much more.