[I'll try to make it simple, ignoring edge cases and real world complexity]
You can't outsource DNS. It's one of the critical piece of networking that must be in every infrastructure.
The common DNS server is BIND. It's been there for 30 years, it's well known, well manageable and well understood. Sysadmins have to know it and manage it. It's especially critical for worldwide multi-site tech organizations.
There is no need for anything else. BIND can do everything and is the most flexible. Some of the alternatives lack some or most of the features (e.g. some type of DNS records).
You should assume that any organization is running it's own DNS servers. (ignore the edge cases).
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In practise for large scale operations, the DNS tree will get very complex.
What the websites changed was only the public DNS server for reddit.com or airbnb.com. It's only the top of the iceberg. There is likely a very complex DNS setup underneath including public domains, private domains, special internal domains, CDN, per datacenter, per continent, etc... which could imply 10 different DNS services.
Who serves the top level public domain is a details. We should assume that the companies put whatever they could in little time to fix the ongoing issue.
> You can't outsource DNS. It's one of the critical piece of networking that must be in every infrastructure.
This is simply not true. For resolvers, you can use your ISPs DNS servers or use a public resolver like Google DNS, OpenDNS, etc. For authoritative DNS there are plenty of hosted (outsourced) offerings like Route53, Dyn, Google Cloud DNS, etc.
This may not work for sufficiently complex organizations, but in my ~20 person SaaS company we have zero DNS servers and it works just fine. We use our ISP's resolvers for client lookups, and Google Cloud DNS for authoritative DNS.
As I said. It's a simplification. I really don't (and can't) get into a long explanation here about how to run a complex DNS infrastructure spanning multiple continents and datacenters ^^
Thing is. You gotta to run your own DNS since the moment you want your own DNS names. Good for you if a simple external DNS service is enough for you, a single 20 people office is not comparable to what the websites mentioned are operating.
You can't outsource DNS. It's one of the critical piece of networking that must be in every infrastructure.
The common DNS server is BIND. It's been there for 30 years, it's well known, well manageable and well understood. Sysadmins have to know it and manage it. It's especially critical for worldwide multi-site tech organizations.
There is no need for anything else. BIND can do everything and is the most flexible. Some of the alternatives lack some or most of the features (e.g. some type of DNS records).
You should assume that any organization is running it's own DNS servers. (ignore the edge cases).
---
In practise for large scale operations, the DNS tree will get very complex.
What the websites changed was only the public DNS server for reddit.com or airbnb.com. It's only the top of the iceberg. There is likely a very complex DNS setup underneath including public domains, private domains, special internal domains, CDN, per datacenter, per continent, etc... which could imply 10 different DNS services.
Who serves the top level public domain is a details. We should assume that the companies put whatever they could in little time to fix the ongoing issue.