What happens when one of the servers, CDN or Recommendations request fails?

Question:

What happens when a server goes down? How do you handle this?
What happens if the CDN stops responding or /recommend request fails and so on.

Answer:

Our monitoring and alerting systems alert us before a server goes down and we quickly add additional resources. Our servers operate in clusters, so in case of a server does go down, its tasks are automatically allocated to other servers in the same cluster, and service is maintained. Additionally, for many services (such as recommendations) if we absolutely can't generate a strategy based recommendation we generate a fallback response, consisting of the most popular products for your site so your customers will not see an empty widget. 
As for the CDN, it is hosted by Akamai, the world's largest CDN provider with a vast network to alternative endpoints so if one is down, the request is quickly transferred to another.