Ok, so here’s another step in the evolution of my Samba4-RODC-based DNS setup. First steps were setting up a Samba4 Read-Only DC in my remote locations, so that DNS would be replicated to that location so that DNS doesn’t fail in case the VPN connection dies. Then we discovered that the SAMBA_INTERNAL DNS backend does not support caching, which unsurprisingly lead to performance problems, so we switched to Samba AD DC with Bind as DNS backend. This setup is quite a bit more complex though, and it seems a bit unstable in the sense that Samba lost its ability to update records in Bind for some reason and we have to “fix” that manually by re-joining the RODC to the domain. Rumor has it that the SAMBA_INTERNAL backend is a lot more stable. So, here’s step three in our evolution: Let’s allow Samba to use SAMBA_INTERNAL, but only run on 127.0.0.1, while communication with the outside world is handled by a bind instance that handles caching and forwards queries for the company domain records to Samba.

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I’ve been looking into Let’s Encrypt DNS verification for a while. Not only because you’re able to obtain wildcard certificates through this method, freeing you from the necessity to obtain an individual certificate for every single one of your subdomains: It also allows you to get a certificate for stuff running on your LAN, provided you’re running it on a subdomain that belongs to you. The problem is though, how do you enable Certbot to automate the DNS server update, without putting a credential in place that would allow full access to all your domains? And what to do if you’re running a server for a domain that doesn’t even belong to you: How can the owner delegate permissions for the verification TXT records to you, without having to give you full access to all their domains? Today I stumbled across a solution: Delegate the _acme-challenge subdomain to a local BIND instance and have Certbot update that. Here’s how.

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Suppose you’re running a few DNS servers spread across multiple locations in your infrastructure, and you want to monitor DNS replication to make sure they’re all on the same page. Here’s an approach on how to do that using Prometheus and a bit of scripting.

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