I am looking at the node-js express example for message-hub on blue mix and am puzzled for why I need to poll message hub from my server. I thought that the whole idea behind a pub-sub model is that I don't have to (over) load my server polling the message service to find out if new messages exist for me to consume. In the example provided, lines 211-213 in the app.js file contain the following:
// Set up an interval which will poll Message Hub for
// new messages on the 'livechat' topic.
produceInterval = setInterval(function() { ...},250);
This now has my server polling message hub every 250 mSec when what I want is to completely avoid a polling model and be notified by message hub when a message exists for me to consume.
in brief: Kafka achieves its scalability by using a consumer-pull model, not a server-push.
in detail: It's worth going through the Kafka documentation first. In particular, your question is answered here http://kafka.apache.org/documentation/#design_pull
HTH, Edo