Docker Isolation Explained: Namespaces, Cgroups, and UnionFS Layers
Enable Docker's namespace isolation by ensuring your containers run with the default security settings and avoid exposing host filesystems.
Run `docker run -it ubuntu bash` to verify namespace isolation and confirm that host processes are not visible inside the container.
Summary
The article explains Docker’s three pillars of isolation: Namespaces provide process isolation, Cgroups enforce resource limits, and UnionFS layers enable fast image reuse. Namespaces trick an app into thinking it is the only process on the host, preventing interference. Cgroups limit RAM and CPU usage to avoid greedy processes starving others. UnionFS layers allow Docker to store a base layer once and snap new top layers for each container, reducing start‑up time. The author demonstrates the ghost protocol by running `docker run -it ubuntu bash` and shows that host processes are invisible inside the container. The article also covers image versus container concepts and the mechanics of Docker’s networking and storage.
Key changes
- Namespaces provide process isolation and prevent interference
- Cgroups enforce resource limits to avoid greedy processes
- UnionFS layers enable fast image reuse and reduce start‑up time
- Docker uses kernel netfilter for packet forwarding
- Image is a read‑only instruction set; container is the runtime instance
- Ghost protocol demonstrates namespace isolation with `docker run -it ubuntu bash`
- Image layers: foundation, tools, personal code
- Container is the active, isolated environment