Docker & Containers

A hands-on tutorial that builds a small Flask app with a Redis counter and runs it with a compose.yaml. It covers health checks, Compose Watch for live updates, persisting data in a named volume, splitting config files and inspecting a running stack with logs and exec.

Official install guide using Docker's apt repository, which installs the engine, CLI, containerd, buildx and compose plugins. It warns that with ufw or firewalld, published container ports bypass your firewall rules, and that Docker only supports iptables-nft and iptables-legacy.

A discussion of how to update a container when its image changes. Answers say to stop the old container first if ports are exposed, manage containers with Compose, rebuild with --no-cache --pull for evergreen tags, and that reusing the same tag breaks image immutability, so explicit version tags are preferred.

Docs on persisting container data with volumes, which Docker calls the preferred mechanism, versus bind mounts that tie you to the host's folder layout. Mentions read-only mounts, subdirectory mounts, volume drivers for NFS/CIFS, and the gotcha that mounting over a non-empty directory hides its existing files. Volumes are not removed automatically when a container is deleted.

Explains how Docker's iptables rules interact with host firewalls. Published ports are handled in the nat table before ufw's chains see the traffic, so a port you publish can be reachable even if ufw seems to block it. The page advises against editing Docker's rules or turning off its iptables management. Treat any published port as exposed to your network.