When One Docker Swarm Replica Became Unreachable Over an Overlay Network: A Production Case With Traefik

Context The incident occurred in the production backend infrastructure of a mobile application. External HTTP traffic was handled by Traefik, deployed on Docker Swarm manager nodes. Traefik ran in swarmMode , used providers.docker , was configured to use the mgp_default network, and had lbswarm disabled so that routing used the required overlay network rather than the Swarm VIP.