server-sent events

 server-sent events  is a DOM API for receiving push notifications from a server via HTTP. Unlike websockets, they're designed for one-way communication between a Web server and a client (Web browser, another Web server or a client application).

Why
Server-sent events are one way to implement real-time comments display on your posts.

How
How does one implement server-sent events, especially in combination with a comment updating system?

(stub, to be filled in)

https://developer.mozilla.org/en-US/docs/Server-sent_events/Using_server-sent_events

server side
One option is using the nginx-push-stream module for nginx. This is e.g. used on chat.indieweb.org.

indieweb.org
The IRC logs use server-sent events to push new IRC messages to the browser in real time.

aaronparecki.com
uses server-sent events to push new posts onto his home page in realtime.

Sweetroll
sweetroll uses server-sent events to show in realtime that the current page has been updated.

Not Supported in IE
While fairly widely supported, server-sent events are currently not supported in IE.
 * MDN lists some polyfill libraries that cover IE and older browsers.