VPS public SSH: enable fail2ban with bantime-increment so brute-force
probers get evicted with exponential backoff (1h → 4h → 16h → 2.7d →
10.7d, capped at 30d). Default jail covers sshd; maxretry=5 in 10m.
server-debug-tools: htop, tcpdump, dnsutils, jq, curl. Imported by
sunken-ship + phantom-ship via flake.nixosModules.server-debug-tools.
These are the practical bits we'd otherwise pick up by enabling
clan.core.enableRecommendedDefaults — but the full clan defaults flip
systemd-networkd/resolved on, which broke dnsmasq + navidrome's resolv
.conf bind-mount on the homelab servers, so we cherry-pick instead.
