Most of the time you change URLs rather than content but it may not apply to real-time scenarios. Some CDN provides distributed key value stores where you can

Most of the time you change URLs rather than content but it may not apply to real-time scenarios. Some CDN provides distributed key value stores where you can push data in seconds, you can also deploy your own code in minutes (for real time changes you would push data, not code). Some providers expose cache purge APIs so you can clear cached data in seconds. They also allow serving cached content while asynchronously revalidating with the Origin so following users get a fresh version. With proper configuration/architecture they are a great way to scale your real-time website.