Then you use > 1 CDN and switch traffic away from the faulty one. Also, if you serve a very large amount (as in different, say tens of thousands of different im

Then you use > 1 CDN and switch traffic away from the faulty one. Also, if you serve a very large amount (as in different, say tens of thousands of different images) of data, 1 % of traffic is not enough to keep the other CDN caches warm. I know of at least one site that works this way which has allowed them to weather CDN outages.