# Security in Cloud-Native Services: A Survey
## 4 Enabling Technologies for Cybersecurity in Cloud-Native Services
### Zero-Trust Architecture (ZTA)  
Moreover, in the past, the traditional perimeter security model was based on the \"trust but verify\" approach. As long as components and equipment belong to a specific network or segmented group, they are considered trustworthy. In such a model, network segmentation, used to establish a trust zone, was assumed to be sufficient. The focus was on whether or not to authorize access to network segments through perimeter security mechanisms such as firewalls. The perimeter model can protect against threats from outside but does not prevent unauthorized lateral movement. Moreover, the implicit perimeter trust model, based on the segmentation of virtual or physical perimeters, does not fit the increasingly complex and dynamic cloud computing environments [87]. Instead, it is imperative to adopt a security model where trust is never granted by default and the principle of least privilege is followed to grant only the minimum necessary privileges, thus limiting the visibility and accessibility of assets [88]. One of the purposes of the zero-trust model is to prevent unauthorized lateral movement as no implicitly trusted zones exist (e.g., no internal network segments are trusted by default). Zero trust intends to provide a more granular and dynamic segmentation of the different resources (i.e., even when network traffic belongs to the same network, it should undergo a validation process) [89].  
According to NIST, the zero-trust architecture must follow the basic zero-trust principles, namely [90]: data, assets, and services are considered resources; communications should be secured regardless of whether networks are considered enterprise-owned or non-enterprise-owned; access to resources is only granted per session; trust should be evaluated before access is granted; access is determined by multiple aspects including the observable state of the user and the service requesting asset; no resource is inherently trusted, there is always an assessment for each access request, which implies monitoring the integrity of the resources.  
Figure 2 illustrates the difference between a perimeter security model and the zero-trust model. In the classical perimeter security model, the authentication focuses on outsider communication to the local area network (LAN), assuming the network is trusted, whereas in the zero-trust model, the network is never trusted and each communication should go through an authentication process. In a service-based architecture and an edge/cloud  
environment, this means that the enforcement of security policies should occur in all network communications between services (and containers).  
Zero trust does not aim to replace the security perimeter model but complements it with a more granular approach to enforce security policies. Whilst zero trust is often linked to authentication and authorization policy enforcement, before granting access to resources, here, its use is based on the idea of having the means for continuous monitoring of all the network traffic (i.e., both north-south and east-west traffic) within a cloud-native environment. Such a continuous evaluation of network traffic is crucial to the timely detection of cyberattacks (e.g., due to compromised components or API abuses) and thus complements additional policy enforcement strategies, fulfilling the zero trust overall principle of \"always verify\".