Making Docker images smaller, safer, and easier to operate in production.
Making Docker images smaller, safer, and easier to operate in production.
Lesson outline
Use minimal base images and multi‑stage builds so you ship only what the app needs—no compilers, test tools, or shells in the final image. Smaller images pull faster and have a smaller attack surface.
Scan images for vulnerabilities regularly and keep base images patched. Treat image updates as part of your normal delivery flow, not a once‑a‑year event.
Set resource limits (CPU/memory) so noisy neighbors do not starve other workloads. Use health checks so orchestrators can restart unhealthy containers automatically.
Log to stdout/stderr instead of local files so your platform (Kubernetes, ECS, etc.) can ship logs to a central system.
Keep configuration out of images: inject settings via environment variables, config maps, or secrets. This lets you promote the same image through multiple environments with different settings.
Use clear tagging conventions (e.g. semantic versions plus git SHA) so you can trace which commit produced which image. Clean up old tags and layers with retention policies to keep registries tidy.
Take an existing Dockerfile and refactor it into a multi‑stage build with a smaller final image. Measure image size and pull time before and after.
Add health checks and resource limits to one of your deployments, and verify how your orchestrator behaves when the container becomes unhealthy or resource‑constrained.
DevOps, platform, and security interviews: expect questions about image scanning, non-root containers, resource limits, and health checks. Candidates who can articulate the security implications of `USER root` stand out.
Common questions:
Strong answer: Explaining that running as root inside a container can enable container escape via kernel exploits. Discussing image scanning as part of CI. Mentioning the principle of least privilege for container filesystem and network.
Red flags: Running containers as root "because it is easier." Not knowing what a health check does. Using the `latest` tag in production. Not scanning images for vulnerabilities.
Quick check · Container best practices
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💡 Analogy
A well-configured container is like a bank vault employee who has a key card that only opens the specific rooms they need, wears a visitor badge, cannot bring personal items in (read-only filesystem), and works in a room with a window so security cameras can see them (health checks, logging to stdout). A poorly configured container running as root with no limits is like that employee having a master key to the whole bank, a bag they can fill with anything, and working in a windowless room with no cameras.
⚡ Core Idea
Container best practices are the application of the principle of least privilege to the container runtime: minimum image size (small attack surface), non-root user (limited blast radius), read-only filesystem (no persistence of malicious files), resource limits (no noisy-neighbour or denial-of-service), and health checks (observable state).
🎯 Why It Matters
Containers are not a security boundary — they share the host kernel. A misconfigured container (running as root, excessive permissions) can compromise the host and every other container on it. Getting container security right is not optional in production; it is the difference between a contained security incident and a full host compromise.
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