gluetun retirement removes the gluetun_vpn_up gauge and the in-cluster gateway pod. Point
VPNTunnelDown at absent(node_network_receive_bytes_total{device=tun0}) — tun0 exists iff the
host OpenVPN tunnel is up (node_network_up unreliable: tun0 operstate=unknown). This also
fires if the gateway node/node-exporter is down (series goes stale). Remove the pod-readiness
EgressGatewayUnhealthy alert — there is no gateway pod under ADR-0015.
Co-Authored-By: Claude Opus 4.8 <[email protected]>