There's something about debugging: the more you have experienced finding the root cause of bugs in the past, the highest the hope and confidence you'll squash the one currently under the microscope. You see I didn't mention "fixing" a bug, because I think finding the root cause of any bug has value per se . Fixing them is a separate adventure. Anyway this week I was entirely bamboozled by this: a Docker container was re-deployed with a different networking configuration. In particular, with Compose, I was dedicating a network for that container (let's say 172.18.0.0/24) separate from the default Docker network (e.g. 172.17.0.0/24). In docker-compose.yml: networks: apps: driver: bridge ipam: driver: default config: - subnet: 172.18.0.0/24 gateway: 172.18.0.1 In the "service" definition I just added this: services: THESERVICE: ...