I don't get it... why do so many major Internet services such as Github, Twitter, SoundCloud and more use only a SINGLE provider of DNS hosting for their DNS records? It used to be that you always made sure you had a second provider doing "secondary DNS" for you. Have people just forgotten this common practice? Or are there other reasons I'm missing?
Probably because until the recent outage it worked well enough; and because a lot of the bigger providers encourage lock-in via their own geographical-options.
Uploading records to multiple providers, via APIs, isn't so hard, but it's something most people don't realize they need until it is too late - or viewed as something that isn't required due to end-user caches.
Thanks. Someone else pointed out to me that some of the advanced features offered by DNS providers, particularly around geographic redirection, is something that is not standardized between providers and so can't be easily duplicated. I can see that - and understand why it would cause you to use only one provider if that was a service you found of value.
Probably because they're worried about keeping two providers in sync throughout the entire world, or they don't have a DNS wizard on staff.
I don't see why sync would be a huge problem; these days moving services usually involves slowly draining active connections from the old addresses while new connections go to the new address. If it takes a day for all the clients to move to the new address then fine, the migration just takes longer.
In hindsight, it's obvious that everyone should use multiple DNS providers. DNS failing has almost never been an issue before, so it's something that a lot of companies didn't expect and were unprepared for.
Thanks. Yes, as you say, it's obvious now... but when you consider that each of those DNS providers has their own globally distributed network involved many servers (via anycast), you can understand why people think that one provider is enough.
Uploading records to multiple providers, via APIs, isn't so hard, but it's something most people don't realize they need until it is too late - or viewed as something that isn't required due to end-user caches.