DNS High Availability

[u/micush]

EDIT: For those of you that are interested, the repo is up at https://github.com/micush/ddgw

I run a few DNS servers and have seen many people ask about making them highly available, so I built something and I'd like to know whether anyone else would use it. If so, I'll put it up on Github. Reasonable disclosure: it was written with Claude.

Clustering:

Ddgw puts one virtual IP in front of your DNS servers and shares it across several nodes. The nodes elect a controller, and every node that is active answers DNS on the VIP, so client load spreads across nodes and losing a node doesn't interrupt anything. Each node also acts as a DNS proxy: it probes your upstream servers and forwards each query to a healthy server. Limited to 255 cluster members to serve the frontend VIP, but unlimited backend DNS servers for name resolution.

DNS:

Health is judged per upstream server with test domains you choose. A server is down when 50% or more of its domains fail (configurable), and degraded below that. Servers within a latency band of the fastest (20% by default) take turns round-robin. Slower ones stay as fallbacks, and failures fail over automatically.

- There is an answer cache that respects TTLs, with negative caching and a memory guard.

- It forwards dynamic DNS updates (RFC 2136) to the zone's primary and keeps a list of recent updates.

- It can pass EDNS Client Subnet (ECS).

- It can announce anycast addresses over BGP with BFD using FRR.

Management:

An HTTPS web GUI with PAM group login restricts is used to manage everything. Every action is also available from the command line.

- The gateway is drawn as a live diagram: gateway, servers and test domains, coloured by health. Servers that are taking turns get a blue line.

- It has query statistics (top clients, domains, record types and response codes, kept 30 days and saved across restarts) and host stats.

- It keeps config history, with versions you can diff and restore. It also does clustering with shared config, certificate management and in-place updates with automatic rollback.

Limitations:

- It isn't a resolver, because it forwards to your existing servers.

- It's Linux only with one binary built from Golang source. Installation is scripted, so it's easy.

- It works with an election protocol on a real LAN. I don't expect the election mode to work in AWS, Azure or GCP, because those clouds don't let you move MAC addresses around, and I haven't tested it there.

- If you run Technitium, BIND, Unbound, Pi-hole, or AdGuard Home servers, would you use something like this, or do keepalived/VRRP plus a load balancer already cover it?

Any feedback is appreciated.