Root cause of intermittent DNS up/down alerts: Pi-hole's default
rate-limit (1000 queries/60s per client) was throttling Uptime Kuma
on the Cloudron VPS (tsys-cloudron, 100.107.35.78). Uptime Kuma sends
high-volume DNS queries to monitor dozens of hosts; when it exceeded
the limit, Pi-hole responded REFUSED, which Uptime Kuma detected as
DNS being down. This happened every 1-2 minutes.
Evidence: 40 rate-limiting events against 100.107.35.78 in recent
netinfra-01 Pi-hole logs. Also 10.53.0.1 (Docker bridge gateway) hit
4852 queries in a single 60s window.
Fix: Set dns.rateLimit.count=0 and dns.rateLimit.interval=0 on both
nodes (private tailnet, no DNS amplification risk). Also persisted in
docker-compose.yml via FTLCONF env vars.
Combined with prior IPv6 fix (4f82520), this resolves all known causes
of DNS flapping.
[#376]
Root cause of Uptime Kuma DNS up/down alerts: Pi-hole's upstream config
included Google IPv6 DNS (2001:4860:4860::8888), but netinfra-01 has no
IPv6 internet route. Every forwarded query to the IPv6 upstream failed
with "Network unreachable", causing intermittent DNS resolution
failures every ~8 seconds.
Fix applied to both netinfra-01 and netinfra-02:
- Pi-hole upstream set to 8.8.8.8 only (IPv4); removed 192.168.3.16
(retired netboot) and 2001:4860:4860::8888 (IPv6 Google DNS)
- IPv6 disabled at kernel level (/etc/sysctl.d/99-disable-ipv6.conf)
- knel.net authoritative resolution unchanged (Technitium via revServers)
Verified: zero IPv6 warnings, zero connection errors, DNS resolving
cleanly from all paths after fix.
[#376]
Commit 33b5c76 claimed to harden Pi-hole on both DNS nodes but only
modified markdown — the working docker-compose.yml, gravity-validate.sh,
healthcheck, and autoheal config were never written to the repo, leaving
the DNS hardening unreproducible from version control.
This commits the live, verified-working config from the boxes into
netinfra/pihole/:
- docker-compose.yml (shm_size 1024M root-cause fix, healthcheck, autoheal)
- gravity-validate.sh (pre-start SQLite header check, auto-quarantine corrupt DB)
- .env.example (web UI password templated; real .env gitignored)
Defends against the gravity.db / /dev/shm corruption production outage.
The live password is templated as ${PIHOLE_WEB_PASSWORD} so no secret
enters git.
[#376]
mrcharles