Container Security: Hardening Images and Protecting the Runtime

The Container Security Chain

Container security begins with the base image and ends with runtime monitoring. Every stage presents an attack surface — and every stage can be secured.

Build Phase: Hardening Images

• Minimal Base Images: Distroless or Alpine instead of Ubuntu — fewer packages, smaller attack surface.
• Non-Root User: Containers should never run as root. Define an unprivileged user in the Dockerfile.
• Read-Only Filesystem: Set the root filesystem to read-only and explicitly mount writable directories.
• No Latest Tag: Pin base image versions to specific digests for reproducible builds.

Registry Phase: Scanning Images

• Admission Controller: Kubernetes admission webhooks can block unsigned or unscanned images.
• Image Signing: Cosign or Notary ensure that only verified images are deployed.

Runtime Phase: Monitor and Restrict

• Security Contexts: Kubernetes security contexts enforce non-root, read-only filesystems, and capability drops.
• Pod Security Standards: The three levels — Privileged, Baseline, and Restricted — as namespace-wide policies.
• Runtime Security: Falco or Sysdig detect suspicious behavior in running containers.

Conclusion

Container security is not a product, but a process. At devRocks, we implement security at every stage — from Dockerfile review to runtime monitoring.