How do you prove to service B that you own the domain?

You don’t need to. Your registrar tells the registry which nameservers you’ve chosen. You specify the nameservers that belong to your DNS provider, which causes DNS clients to query that DNS provider.

There’s nothing stopping you from paying for service with a DNS provider for a domain you don’t own, but nobody will actually query those nameservers for your domain, so it doesn’t matter.

You usually need to update the name servers with service A to point to service B.

I reached that by accident. Service B for DNS was just a more pleasant product to use than service A, and service A didn't offer certain features I needed for emails.

To bring it back on topic, this made it easy when I switched service A from Gandi to something else a year or two ago because a few things I was seeing from them "smelled funny." I don't remember the details, just that I wanted to switch.

Same, swapped over to PorkBun. Much more pleasant experience.

DNSControl[1] or another similar tool also helps a lot when moving. My DNS records are configured by a small JavaScript file in a git repository, and I can very easily point it at another DNS provider.

[1]: https://dnscontrol.org/

Could you disclose what B is? Pretty much please?

DNS Made Easy - perhaps too costly now, and not the best, but I use them since 10 years and had no issue with them. But might be oversized, I've started to use them for a startup b/c they had failover to point to another load balancer if one balancer/data center is down.

I've been using ZoneEdit for years, and they have a limited free tier. It's been great for my admittedly tiny use cases.

Which services do you use specifically?

Namecheap (I want to get off) and DNS Made Easy (I've started to use them with our startup for reliability)

Huh, I've been happy with Namecheap for a few years now. But I never looked that hard.

Suggestions for service B? Every single service I can find always seems such a pain to go in and add a subdomain and change something.

If you just care about user interface, Cloudflare is pretty stellar.

Honestly I think it depends where you are deploying to. I was previously using Netlify DNS for instance since most of my domains had static websites hosted on Netlify, this meant that they could manage quite a lot of records for me, I was also a fan of having CNAME-flattening which isn't available at domains.google (for reference I'm using the .dev TLD which is owned by the Google Registrar), but I've recently switched to using Google's name servers and even though I have to use a hard coded IP for the Netlify load balancer and I lost CNAME flattening I'm pretty the DNS requests are going MUCH faster (as in a few tens of milliseconds faster LOL). The reason I'm using Google's name server is because Netlify DNS doesn't support DNSSEC which for me is simply absurd in 2023.

Anyways, if you don't have a specific reason to pick any specific nameserver go with the easiest one or if you want to have the most features and portability go with Cloudflare.

Almost none of the most popular/important zones on the Internet aren't signed, so there is little impetus for providers to support DNSSEC. IPv6 is a more annoying lapse.

Digitalocean.

Same.. API access is pretty nice too... I run a simple script for dyndns at home.

I've been relatively happy using digital ocean for DNS.

Even run a dyndns script to have a subdomain for my wireguard connections to home.

I use service A for domains, service B for DNS, service C for emails, and service D for WHOIS privacy protections.

I have this, but it's not quite as fully seperated out, as server B is also my server host.