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Zero-trust networks in Kubernetes, cloud-native applications

The complexity of corporate networks and the distributed applications in them have evolved, and the threat models and the methods leveraged to deepen infiltration have followed suit. Secure perimeters can only serve as a first-line defense to protect internal networks, not a comprehensive strategy for the protection of infrastructure and data. Robust security requires a combination of controls and strategies.

Zero-trust networking can serve as an important piece of the security puzzle by focusing on increasing the safety of internal application traffic. This model overturns the long-held tenet that all traffic inside a firewalled network is authentic with the opposite assumption: no network connections should be considered safe until they prove otherwise.

Traditionally, network administrators worked under the assumption that every entity, whether application, server, or piece of networking software or hardware, found in their internal networks belonged there and could be trusted. Some applications did not require authentication of client connections or relied on static, shared credentials, e.g. a password for a database. All applications had to handle any authentication or authorization schemes they needed, if they used any at all. Often, internal network connections, even those for sensitive services, did not use any encryption.

More than a few corporate networks still follow this pattern. However, a single bad actor that can be placed inside this lax environment, whether through a direct hack, a trojan horse applied accidentally by an authorized individual, or simply a hole in a network firewall, can wreak havoc by taking full advantage of this implicit network of trust. The possibilities may not be endless, but they are predictable. From sniffing of plaintext network packets to discovering application passwords to databases or other critical systems all the way to gaining control of network equipment, this scenario opens the door to unacceptable risks, including data exfiltration or loss.

Zero-trust forms the basis of a growing number of security-first production infrastructures. Instead of assuming every entity on a network can be trusted without verification, it assumes nothing can, not even the network infrastructure itself. The zero-trust framework does not offer a prescriptive implementation or specific set of technologies to use. Rather, it describes a set of principles and goals, leaving the specific technical details of implementation to each organization.

Zero-trust architectures

Zero-trust architectures generally follow these principles:

  • Security controls should apply equally to all entities, whether software or hardware, regardless of their network location.
  • Network connections should be authenticated at both ends, by the server and the client. Client authentication by the server is generally expected now, but clients should also verify that they have connected to a valid server. Connections should be reauthenticated and requests should be reauthorized as needed when they span more than a single transaction.
  • Authorization grants should follow the principle of least privilege, allowing only the bare minimum permissions required for a client’s workload.
  • All network connections and transactions should be subject to continuous monitoring for analysis.

Implementing Zero-trust model in Kubernetes

What would a zero-trust model look like in a Kubernetes cluster? While no single methodology for implementing zero-trust principles within a Kubernetes cluster exists, service meshes have emerged as a popular solution for many of the architecture’s goals.

Service meshes create a virtualized network layer to connect and control distributed application services. While most service mesh solutions initially did not focus on network security, but rather on facilitating and managing intelligent service discovery and request routing, the most popular open-source projects now offer features that fit in a zero-trust architecture. As many service meshes attempt to create an overlay that does not require modification of individual applications, they eliminate much of the burden of making significant changes to enable strict authentication and authorization controls.

Service meshes that support Kubernetes typically use decentralized, point-to-point routing by giving each individual cluster pod its own proxy instance. These proxies can manage client TLS certificates, which the proxy can use to prove its identity when making connections to other services or receiving connections from other clients. This use of TLS certificates to provide proof of identity on both the client and server sides is called mutual Transport Layer Security (mTLS). mTLS, besides performing connection authentication, also serves to encrypt the network connection. In addition to authentication and encryption over the wire, different service meshes support different authorization sources, ranging from static lists to integrations with third-party single sign-on or other services.

Service meshes do not provide a complete zero-trust solution for Kubernetes clusters, but they do offer a number of its core benefits. Even if you cannot achieve a perfect zero-trust architecture in your Kubernetes clusters, any incremental changes you make in that direction will help to protect your cluster and its workloads.

Last updated: May-31-2020