vh
959a743256
Operator's design, and a better one. Once the FV SNAT rules landed, fv-ml1's mesh membership was redundant for routing and its only remaining value was as a second way in. Keeping it enrolled bought a standing second door; joining on demand buys the same recovery path without one. normal tailscaled stopped + disabled; fleet reached via the gateway SNAT fault nh3-dev / nh3-docker unreachable while the WAN is up action start tailscaled + tailscale up -> reachable at its 100.64.x address fv-ml1 is now off the mesh and its node record deleted. Verified it still reaches NH3, ESH, Anaheim, Irvine and the internet on the SNAT path alone, then the break-glass fired on cue (counted 1..4, joined at 5 as 100.64.0.10), answered ping and ssh from nh3-dev, and was closed again cleanly. No auto-leave, deliberately: once open the door stays open until a human runs systemctl disable --now tailscaled. A watchdog that re-closes on recovery flaps, and a flapping recovery path is down exactly when someone finally looks. It also skips entirely when already on the mesh, which is what makes it idempotent after firing. The question exposed a hole worth more than the redesign. The stored rejoin key was one of the 2026-09-12 FV cutover keys, expiring 2026-09-19 -- a break-glass credential that dies in four days and fails silently at the only moment it matters. Replaced with a dedicated 1-year reusable key (headscale ID 8, expires 2027-09-15), vaulted as fv-ml1/headscale-breakglass-key, root:600 on the host. That also closes the standing self-join risk rather than trading it: the two stale reusable keys (IDs 5, 6) are expired, so the mesh now has exactly one live reusable key -- purpose-built, on a host we control -- instead of two orphans nobody owned. Rejoin uses --accept-routes=false and the reason is in the script: on 2026-09-14 tailscale up --accept-routes on this box accepted its OWN subnet from the gateway and black-holed it. That happened with a human watching; here it runs unattended, during an incident, on a box already in trouble.
95 lines
4.2 KiB
Bash
95 lines
4.2 KiB
Bash
#!/bin/sh
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# fv-mesh-watchdog — BREAK-GLASS: join the mesh when fv-ml1 loses the fleet.
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#
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# ⭐ INVERTED DESIGN (operator, 2026-09-15). fv-ml1 is normally OFF the mesh: its
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# cross-site traffic is carried by outbound SNAT on the FV OPNsense gateway
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# (docs/runbooks/fv-to-ana-nat.md), so mesh membership is redundant for routing
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# and its only value is as a SECOND way in when the first one breaks. Keeping it
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# permanently enrolled bought a standing second door; joining ON DEMAND buys the
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# same recovery path without one.
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#
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# This is therefore not a "restore Tailscale" watchdog. It is a door that opens
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# when the normal path is gone.
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#
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# normal tailscaled stopped+disabled; fleet reached via the gateway's SNAT
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# fault FLEET_ANCHORS unreachable while the WAN is up
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# action start tailscaled and `tailscale up` -> the box is reachable at its
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# mesh address even though its LAN path is broken
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#
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# ⚠ TWO ANCHOR CLASSES, and they must not share a failure mode:
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# WAN_ANCHOR plain internet. If THIS is down the site uplink is gone,
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# Tailscale cannot fix it, and we do nothing -- thrashing
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# during an ISP outage turns a wait into an incident.
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# FLEET_ANCHORS hosts reachable ONLY through the gateway's SNAT path. Their
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# loss is exactly the fault this exists for.
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#
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# ⚠⚠ THE REJOIN MUST USE --accept-routes=false. On 2026-09-14 a
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# `tailscale up --accept-routes` on this box accepted 10.251.0.0/16 from the
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# gateway -- its OWN subnet -- and routed the local network through the tunnel,
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# black-holing it. That happened with a human watching. Here it would run
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# unattended, during an incident, on a box already in trouble.
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#
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# ⚠ NO AUTO-LEAVE. Once the door is open it stays open until a human closes it
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# (`systemctl disable --now tailscaled`). A watchdog that re-closes on recovery
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# flaps, and a flapping recovery path is worse than none -- it would be down
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# exactly when someone finally looked.
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#
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# Disable for planned work: touch /etc/fv-watchdog.disable
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set -u
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STATE=/var/lib/fv-mesh-watchdog
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CONF=/etc/fv-mesh-watchdog.conf
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DISABLE=/etc/fv-watchdog.disable
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FAIL_THRESHOLD=5
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WAN_ANCHOR=1.1.1.1
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FLEET_ANCHORS="10.100.10.50 10.100.50.40" # nh3-dev, nh3-docker
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LOGIN_SERVER=https://headscale.phasefinal.com
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[ -r "$CONF" ] && . "$CONF"
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log() { logger -t fv-mesh-watchdog "$*"; printf '%s fv-mesh-watchdog: %s\n' "$(date -Is)" "$*"; }
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if [ -e "$DISABLE" ]; then log "disabled by $DISABLE — no action"; exit 0; fi
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mkdir -p "$STATE"; COUNT_FILE="$STATE/consecutive_failures"
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[ -f "$COUNT_FILE" ] || echo 0 > "$COUNT_FILE"
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count=$(cat "$COUNT_FILE" 2>/dev/null || echo 0)
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# Already on the mesh? Then the door is open and there is nothing to do. This is
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# also what makes the script idempotent after it has fired.
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if [ "$(systemctl is-active tailscaled 2>/dev/null)" = active ] \
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&& tailscale status >/dev/null 2>&1; then
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[ "$count" -ne 0 ] && echo 0 > "$COUNT_FILE"
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exit 0
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fi
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ping -c 2 -W 3 "$WAN_ANCHOR" >/dev/null 2>&1 && wan=up || wan=down
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if [ "$wan" = down ]; then
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[ "$count" -ne 0 ] && log "uplink down — not a fleet-path fault, counter reset"
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echo 0 > "$COUNT_FILE"; exit 0
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fi
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# Any fleet anchor answering means the normal path works.
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fleet=down
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for a in $FLEET_ANCHORS; do
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if ping -c 2 -W 3 "$a" >/dev/null 2>&1; then fleet=up; break; fi
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done
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if [ "$fleet" = up ]; then
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[ "$count" -ne 0 ] && log "fleet path recovered after $count failure(s)"
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echo 0 > "$COUNT_FILE"; exit 0
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fi
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count=$((count + 1)); echo "$count" > "$COUNT_FILE"
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log "fleet unreachable via the gateway path while WAN is up ($count/$FAIL_THRESHOLD) — anchors: $FLEET_ANCHORS"
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[ "$count" -lt "$FAIL_THRESHOLD" ] && exit 0
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log "THRESHOLD REACHED — opening the break-glass mesh path"
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echo 0 > "$COUNT_FILE"
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systemctl start tailscaled 2>&1 | while read -r l; do log " start: $l"; done
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if [ -r "$STATE/authkey" ]; then
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tailscale up --login-server "$LOGIN_SERVER" --authkey "$(cat "$STATE/authkey")" \
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--accept-routes=false --hostname "$(hostname -s)" 2>&1 | while read -r l; do log " up: $l"; done
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log "mesh path OPEN — reach this host at its 100.64.x address; close with 'systemctl disable --now tailscaled'"
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else
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log " NO $STATE/authkey — cannot join. The break-glass path is UNARMED."
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fi
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