When an HN post is popular, we sometimes crash small websites/blogs.

How about a URL Shortener that caches the page at the time the shortened URL is created?

Then, when the short url is used, the service attempts to reach the site, if it fails, automatically inform user & redirect them to cached page.

Or, the service can attempt to reach the page periodically (once/ couple minutes), if fails, redirect all users to cached page until next attempt in a couple minutes. This period can be based on number of users clicking on the url. Once the link is no longer very popular, the service will have a fairly long time between attempts.