Using global variables in my node.js program configuration
You say you're using globals because "I have added a watch function to watch for the changes in the config.json file". You don't need globals for this. If you declare the variables at the top level, like you've done with http and server, they'll be accessible everywhere in your script, including inside the anonymous function where you're using them.* You could get rid of the (function() { ... })(); wrapper round the first bit (not sure why you've wrapped that bit) and then declare them there.

"I know using global variables in JavaScript is bad practice." Using global variables in any language is bad practice if you can avoid it.

*A function like this, which uses variables declared outside the function, is called a "closure".