Securing Kubernetes

In Chapter 3, High Availability and Reliability, we looked at reliable and highly available Kubernetes clusters, the basic concepts, the best practices, how to do live updates, and the many design trade-offs regarding performance and cost.

In this chapter, we will explore the important topic of security. Kubernetes clusters are complicated systems composed of multiple layers of interacting components. Isolation and compartmentalization of different layers is very important when running critical applications. To secure the system and ensure proper access to resources, capabilities, and data, we must first understand the unique challenges facing Kubernetes as a general-purpose orchestration platform that runs unknown workloads. Then we can take advantage of various securities, isolation, and access control mechanisms to make sure the cluster, the applications running on it, and the data are all safe. We will discuss various best practices and when it is...

Understanding Kubernetes security challenges

Kubernetes is a very flexible system that manages very low-level resources in a generic way. Kubernetes itself can be deployed on many operating systems and hardware or virtual-machine solutions, on-premises, or in the cloud. Kubernetes runs workloads implemented by runtimes it interacts with through a well-defined runtime interface, but without understanding how they are implemented. Kubernetes manipulates critical resources such as networking, DNS, and resource allocation on behalf of or in service of applications it knows nothing about. This means that Kubernetes is faced with the difficult task of providing good security mechanisms and capabilities in a way that application developers and cluster administrators can utilize, while protecting itself, the developers, and the administrators from common mistakes.

In this section, we will discuss security challenges in several layers or components of a Kubernetes cluster: nodes, network...

Hardening Kubernetes

The previous section cataloged and listed the variety of security challenges facing developers and administrators deploying and maintaining Kubernetes clusters. In this section, we will hone in on the design aspects, mechanisms, and features offered by Kubernetes to address some of the challenges. You can get to a pretty good state of security by judicious use of capabilities such as service accounts, network policies, authentication, authorization, admission control, AppArmor, and secrets.

Remember that a Kubernetes cluster is one part of a bigger system that includes other software systems, people, and processes. Kubernetes can't solve all problems. You should always keep in mind general security principles, such as defense in depth, a need-to-know basis, and the principle of least privilege. In addition, log everything you think may be useful in the event of an attack and have alerts for early detection when the system deviates from its state. It may...

Running a multi-user cluster

In this section, we will look briefly at the option to use a single cluster to host systems for multiple users or multiple user communities (which is also known as multi-tenancy). The idea is that those users are totally isolated and may not even be aware that they share the cluster with other users. Each user community will have its own resources, and there will be no communication between them (except maybe through public endpoints). The Kubernetes namespace concept is the ultimate expression of this idea.

The case for a multi-user cluster

Why should you run a single cluster for multiple isolated users or deployments? Isn't it simpler to just have a dedicated cluster for each user? There are two main reasons: cost and operational complexity. If you have many relatively small deployments and you want to create a dedicated cluster for each one, then you'll have a separate master node and possibly a three-node etcd cluster for each one...

Summary

In this chapter, we covered the many security challenges facing developers and administrators building systems and deploying applications on Kubernetes clusters. But we also explored the many security features and the flexible plugin-based security model that provides many ways to limit, control, and manage containers, pods, and nodes. Kubernetes already provides versatile solutions to most security challenges, and it will only get better as capabilities such as AppArmor and various plugins move from alpha/beta status to general availability. Finally, we considered how to use namespaces to support multi-user communities or deployments in the same Kubernetes cluster.

In the next chapter, we will look in detail into many Kubernetes resources and concepts, and how to use them and combine them effectively. The Kubernetes object model is built on top of a solid foundation of a small number of generic concepts such as resources, manifests, and metadata. This empowers an extensible...

References

• https://www.stackrox.com/post/2019/04/setting-up-kubernetes-network-policies-a-detailed-guide/
• https://github.com/ahmetb/kubernetes-network-policy-recipes
• https://jeremievallee.com/2018/05/28/kubernetes-rbac-namespace-user.html