Security Hardening a Kubernetes Cluster#

This operational sequence takes a default Kubernetes cluster and locks it down. Phases are ordered by impact and dependency: assessment first, then RBAC, pod security, networking, images, auditing, and finally data protection. Each phase includes the commands, policy YAML, and verification steps.

Do not skip the assessment phase. You need to know what you are fixing before you start fixing it.

Phase 1 – Assessment#

Before changing anything, establish a baseline. This phase produces a prioritized list of findings that drives the order of remediation in later phases.

Security Contexts, Seccomp, and AppArmor#

Security contexts control what a container can do at the Linux kernel level: which user it runs as, which syscalls it can make, which files it can access, and whether it can escalate privileges. These settings are your last line of defense when a container is compromised. A properly configured security context limits the blast radius of a breach by preventing an attacker from escaping the container, accessing the host, or escalating to root.

SSH Key Management#

SSH keys replace password authentication with cryptographic key pairs. The choice of algorithm matters:

Ed25519 (recommended): Based on elliptic curve cryptography. Produces small keys (256 bits) that are faster and more secure than RSA. Supported by OpenSSH 6.5+ (2014) – virtually all modern systems.

ssh-keygen -t ed25519 -C "user@hostname"

RSA 4096 (legacy compatibility): Use only when connecting to systems that do not support Ed25519. Always use 4096 bits – the default 3072 is adequate but 4096 provides a safety margin.