Hello World 503 server not available error

[Michael Malgeri]

Hi,

I'm playing around with the HelloWorld example for Apache Nifi through the 
Apache Nifi dummies book.
I can start the HelloWorld example,  the red box for each process turns to a 
green arrow, but when I navigate in a browser to localhost:6688 it time out 
with a 503 server not available error.
Any tips?
Thank you.
Michael