DNS
Definition
Name-to-record resolution — the phonebook of the internet (and every private network).
Record types that matter
- A / AAAA — name to IPv4/IPv6
- CNAME — alias
- MX — mail server
- TXT — verification, SPF, DKIM
- SRV — service location
- NS / SOA — authority
Where it appears
🌐 Networking
- Authoritative — BIND, PowerDNS, NSD
- Recursive resolvers — Unbound, dnsmasq
- Split-horizon — different answers for internal vs external clients
🐧 Linux
- systemd-resolved — stub resolver
- NetworkManager — manages
/etc/resolv.conf - nsswitch.conf — resolution order
☁️ Cloud
- AWS Route 53 — public zones, private zones (VPC-scoped), health checks, routing policies (failover, latency, geo, weighted)
- Azure DNS / Private DNS Zones — equivalent
📦 Containers
- CoreDNS — in-cluster DNS for Kubernetes
- Service discovery —
svc.namespace.cluster.local