Bridge

How a container’s room gets out — Docker’s network modes compared with real namespace numbers, inside/outside pairing by @ifN, docker0 joined to the NIC by routing and NAT, CNM vs CNI and one CNI plugin call, VXLAN overlay, and one Go server knocked on from four places: another container, the host, another machine, and a container sharing its room.

What a container actually is on an Ubuntu VM — three problems that VMs and containers each solve, the runtime stack from dockerd and kubelet down to runC, why runC vanishes and containerd-shim stays as the parent, the six namespaces and one cgroup directory seen through /proc.