In the fast-paced world of Cloud Native, the transition from "code commit" to "production pod" is often a fragmented journey. As platform engineering matures, the responsibility for security has shifted from being a final gatekeeper to a continuous thread woven into the software lifecycle. Gone is the era where a simple image scan was enough. Today’s threats require a multi-layered defence-in-depth strategy that treats security as an automated, immutable property of the platform. This talk provides a tactical blueprint for engineers looking to secure their platforms from the supply chain to runtime.