What is the principle of least privilege in Docker?
Why Interviewers Ask This
This question targets practical, hands-on experience with Docker. Interviewers want to see if you've worked with these concepts in real projects, not just read about them. Strong answers include concrete examples.
Answer
The principle of least privilege in Docker means giving containers only the capabilities and access they need — no more. Applied to Docker: (1) Non-root user: use USER in Dockerfile; set runAsNonRoot: true in Kubernetes; (2) Read-only filesystem: docker run --read-only myapp — container cannot write to its filesystem (mounts tmpfs for /tmp if needed); (3) Drop capabilities: Linux capabilities grant specific privileges. Docker grants ~14 by default. Drop all and add only needed: docker run --cap-drop ALL --cap-add NET_BIND_SERVICE myapp (NET_BIND_SERVICE lets you bind to ports <1024 without root); (4) No privileged mode: never use --privileged unless absolutely necessary (gives container nearly all host capabilities); (5) No host namespaces: avoid --network host, --pid host, --ipc host unless necessary; (6) Minimal images: fewer packages = smaller attack surface; (7) seccomp profiles: restrict system calls the container can make; (8) AppArmor/SELinux: mandatory access control profiles; (9) Immutable volumes: mount volumes as read-only when container only needs to read: -v data:/app/data:ro; (10) Limited resource access: set CPU and memory limits to prevent resource exhaustion.
Pro Tip
Demonstrate both theoretical understanding and practical experience. Say what it is, then give an example of how you actually used it in a Docker codebase.