Basic Principles of Zero-Trust: Continuous Security Is Better Than Perimeter

Traditionally security is viewed as a perimeter model: a great big strong wall keeps the bad out and lets the good live its life inside.
However, a better model is to view security as a continuous task. Defense in Depth. Make each bit prove itself to its neighbour (and make the neighbour prove itself back).
Mutual TLS.
SPIFFE.
Client Certificates.
Workload isolation.

Perimeter