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mrcharles d6988bb35f fix(netinfra): disable Pi-hole rate-limiting causing Uptime Kuma flapping

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]

2026-08-06 13:59:45 -05:00

2.7 KiB

Raw Blame History

netinfra/pihole/ — Pi-hole recursive DNS (pfv-netinfra-01/02)

Redmine: #376 (up/down alerts + commit hardening) · #357 (cluster build, closed)

Pi-hole v6 runs as the recursive resolver on port 53 of both DNS nodes. Technitium (tsys-dns) runs as the authoritative server on port 5300; the two share the dnsnet Docker network so Pi-hole can conditional-forward knel.net zones to Technitium.

Hardening (defense-in-depth against gravity.db corruption)

The operator hit a production outage when Pi-hole's /dev/shm was too small, corrupting gravity.db. The live config on both nodes now includes:

shm_size: 1024M — fixes the root cause (default 64M was too small).
gravity-validate.sh — entrypoint that checks the SQLite header of gravity.db before start; auto-moves a corrupt/empty DB aside so Pi-hole can regenerate it cleanly.
Healthcheck — dig +norecurse @127.0.0.1 pi.hole + gravity.db non-empty; fails the container if DNS or the DB is broken.
autoheal sidecar — restarts any container labeled autoheal=true that goes unhealthy.

Deploy

The compose reads the web UI password from a gitignored .env:

cd netinfra/pihole/
cp .env.example .env          # then edit .env and set PIHOLE_WEB_PASSWORD
docker compose up -d

Files are deployed to /home/localuser/services/pihole/ on each node. Volumes (./etc-pihole, ./etc-dnsmasq.d) hold the persistent state.

IPv6 disabled + Rate-limiting disabled

IPv6

Both netinfra nodes run IPv4-only. IPv6 is disabled at the kernel level (/etc/sysctl.d/99-disable-ipv6.conf) because netinfra-01 has no IPv6 internet route, and Pi-hole's default IPv6 upstream (Google 2001:4860:4860::8888) was causing continuous "Network unreachable" errors + intermittent DNS failures detected by Uptime Kuma. The upstream is now 8.8.8.8 (IPv4 only).

Rate-limiting

Pi-hole's default rate-limit (1000 queries / 60 seconds per client) was the root cause of Uptime Kuma DNS flapping. Uptime Kuma runs on the Cloudron VPS (tsys-cloudron, 100.107.35.78) and sends high-volume DNS queries to monitor dozens of hosts. When it exceeded 1000 queries/60s, Pi-hole responded with REFUSED, which Uptime Kuma detected as DNS being down. Rate-limiting is now disabled (count=0, interval=0) since this is a private tailnet with no risk of DNS amplification attacks.

Verify

dig @127.0.0.1 +short google.com        # recursive
dig @127.0.0.1 +short git.knownelement.com   # knel.net via Technitium forward
docker inspect pihole --format '{{.State.Health.Status}}'

2.7 KiB Raw Blame History