Even the most secured Kubernetes cluster can have security issues in case the underlying OS is not correctly hardened. In this talk, we will present the best practices to harden and secure your container hosts from the delivery to the different environments to ensure reliability, security and performance. Through an actual live example, we will introduce how Flatcar Container Linux is first built around security, and uses the hardening practices. From SELinux configuration to audit logs passing by its package management - let's see how this container optimized OS distro can contribute to reduce the surface attack and mitigating threats.