Bash script to install heartbeat for healthchecks.io

#!/usr/bin/env bash

set -Eeuo pipefail

readonly ENV_FILE="/etc/pi-heartbeat.env"
readonly SERVICE_FILE="/etc/systemd/system/pi-heartbeat.service"
readonly TIMER_FILE="/etc/systemd/system/pi-heartbeat.timer"

usage() {
    cat <<'EOF'
Usage:
  sudo ./install-heartbeat.sh <ping-url>

Example:
  sudo ./install-heartbeat.sh https://hc-ping.com/your-check-uuid
EOF
}

if [[ ${EUID} -ne 0 ]]; then
    echo "Error: run this installer with sudo." >&2
    usage >&2
    exit 1
fi

if [[ $# -ne 1 ]]; then
    usage >&2
    exit 1
fi

ping_url=$1

case "$ping_url" in
    https://* | http://*) ;;
    *)
        echo "Error: ping URL must begin with https:// or http://." >&2
        exit 1
        ;;
esac

if [[ "$ping_url" == *$'\n'* || "$ping_url" == *$'\r'* || "$ping_url" == *' '* ]]; then
    echo "Error: ping URL contains invalid whitespace." >&2
    exit 1
fi

if ! command -v systemctl >/dev/null 2>&1; then
    echo "Error: systemd is required." >&2
    exit 1
fi

if ! command -v curl >/dev/null 2>&1; then
    echo "curl is missing; installing it..."
    apt-get update -qq
    apt-get install -y curl
fi

umask 077
printf 'PING_URL=%s\n' "$ping_url" >"$ENV_FILE"
chown root:root "$ENV_FILE"
chmod 0600 "$ENV_FILE"

cat >"$SERVICE_FILE" <<'EOF'
[Unit]
Description=External availability heartbeat
Wants=network-online.target
After=network-online.target

[Service]
Type=oneshot
EnvironmentFile=/etc/pi-heartbeat.env
ExecStart=/usr/bin/curl --fail --silent --show-error --max-time 10 --retry 2 --retry-delay 3 ${PING_URL}
TimeoutStartSec=45
NoNewPrivileges=true
PrivateTmp=true
ProtectHome=true
ProtectSystem=strict
EOF

cat >"$TIMER_FILE" <<'EOF'
[Unit]
Description=Send external availability heartbeat every minute

[Timer]
OnBootSec=2min
OnUnitActiveSec=1min
AccuracySec=10s
RandomizedDelaySec=10s
Unit=pi-heartbeat.service

[Install]
WantedBy=timers.target
EOF

chown root:root "$SERVICE_FILE" "$TIMER_FILE"
chmod 0644 "$SERVICE_FILE" "$TIMER_FILE"

systemctl daemon-reload
systemctl enable --now pi-heartbeat.timer

echo "Sending the first heartbeat..."
if systemctl start pi-heartbeat.service; then
    echo "Heartbeat installed and first check-in succeeded."
    echo "Timer status:"
    systemctl --no-pager --full status pi-heartbeat.timer || true
else
    echo "Heartbeat was installed, but the first check-in failed." >&2
    echo "Inspect it with: journalctl -u pi-heartbeat.service -n 30 --no-pager" >&2
    exit 1
fi