Ask HN: What do you use for load balancing and failover?

It's been 3 years since this question last appeared on HN (http://news.ycombinator.com/item?id=180311). Time for an update.

What software or hardware do you use for load balancing? Are you happy with it? How does it compare to alternatives?

How do you achieve high availability? How do you handle the failure of a machine, a network connection or a data center?