Docker daemon — alert when dockerd hangs
docker info hangs >30 s — the daemon is in a split-brain state. Containers keep running (kernel holds the namespaces), but you cannot deploy a new release. systemctl status shows active.
Recipe
#!/usr/bin/env bash
# /etc/cron.d/docker-hang
# */2 * * * * root /opt/docker-hang.sh
TIMEOUT=${TIMEOUT:-15}
# Use timeout — `docker info` will hang forever if daemon is wedged
if timeout "$TIMEOUT" docker info >/dev/null 2>&1; then
echo "OK"
exit 0
fi
curl -fsS "$HEARTBEAT_URL" --data "docker_hang=true,timeout=${TIMEOUT}s"
exit 2Same thing in Enterno.io
Set up an Enterno heartbeat on a 2-minute schedule — learn about a daemon hang inside 4 minutes, not "the next morning when the first deploy fails CI".
Related recipes
A container OOM-kills, the restart policy revives it — no external signal until users complain.
The clock drifts (timesync hung, the NTP provider went down) — TOTP starts failing, JWTs with iat in the future get rejected, logs go out of order.
Anonymous image pulls hit Docker Hub limits (100/6h per IP) — CI starts failing with TooManyRequests. Usually visible only after you are already over.