HI lionel,
you bind a cloudant nosql database to the app in the kubernetes cluster but hello-world app can't communicate with the db.
Could you create a new todo app binded to this db or add Watson tone analyzer service to the hello-world app ?

Leverage the existing app
https://github.com/watson-developer-cloud/conversation-simple

The repo where the Conversation lab is pointing to at step #6 is not providing a Deploy to Bluemix button anymore, it's now steps to follow.

Lionel,
NodePort number is missing when you check out the url:

The NodePorts are randomly assigned when they are generated with the expose command, but within 30000-32767. In this example, the NodePort is 30872.

Get the public IP address for the worker node in the cluster.

bx cs workers <cluster_name_or_id>
Output:

Listing cluster workers...
OK
ID Public IP Private IP Machine Type State Status
dal10-pa10c8f571c84d4ac3b52acbf50fd11788-w1 169.47.227.138 10.171.53.188 free deployed Deploy Automation Successful
Open a browser and check out the app with the following URL:

http://<Public_IP_address>:<NodePort_Number>
In this exemple => http://169.47.227.138:30872