Summary

The website content discusses the Service Account Token Volume Projection feature in Kubernetes, introduced in version 1.2, which enhances security for inter-pod communication by providing tokens with expiration times, specific issuers, and intended audiences, mounted as projected volumes.

Abstract

In Kubernetes, the Service Account Token Volume Projection is a security feature that allows for more secure communication between pods within a cluster. It was introduced in Kubernetes 1.2 to address the limitations of traditional service account tokens by providing tokens that expire, specifying the issuer and the audience for whom the token is intended. This feature is implemented by the kubelet as a volume plugin, which automatically rotates the tokens as they approach expiration. The projected volume combines tokens for different services within the cluster, enabling a pod to use a specific token to communicate with selected services, thus enhancing the security model of microservices architectures.

Opinions

The author views the Service Account Token Volume Projection as a significant advancement in Kubernetes security, particularly for microservices architectures.
The feature is seen as a solution to the problem of secure communication between pods, which is essential for modern applications.
The author emphasizes the flexibility of the feature, as it allows for the integration of external authentication systems, such as Google's, into the Kubernetes cluster.
The article suggests that the rotation of tokens by the kubelet contributes to a more dynamic and secure environment by minimizing the risk associated with long-lived credentials.

Understanding service account token volume projection in Kubernetes

This is the second post of my series of posts where I discuss security in Kubernetes. In the first post, I wrote about service accounts, what they are made up of and their usage.

As mentioned in the first post a service account is made up of a secret. This secret contains a ca.crt file and a jwt token. This token is then mounted into the pod. The pod uses this token as a Bearer token to authenticate its API requests to the API server. While a service account solves the problem of communication between a pod and the API server, there was a need to solve the problem of communication between two different pods running in a cluster.

In Kubernetes 1.2 a new feature was introduced Service Account Token Volume Projection. This feature allows a token issued by the TokenRequest API of Kubernetes to be mounted into the pod as a projected volume. Unlike the service Account token, this token will have an expiry time. This token will also have additional fields of issuer and audience . The issuer field will refer to the issuing service that has issued the token, in the above setup this will be api however we can configure an external issuing source. The audience field will refer to the service that will consume this token. This means that the pod will use this particular token to talk to only a selected number of services in the cluster.

The creating and projection of the service account token is managed by a volume plugin implemented in the kubelet . As the toke approaches expiration, the kubeletvolume plugin will rotate the service account token.

Service Account Token Volume Projection is mounted into a pod as projected volume.

apiVersion: v1

kind: Pod

metadata:

name: nginx

spec:

  containers:

  - image: nginx

    name: nginx

    volumeMounts:

    - mountPath: /var/run/secrets/tokens

      name: vault-token

  serviceAccountName: build-robot

  volumes:

  - name: vault-token

    projected:

      sources:

      - serviceAccountToken:

          path: vault-token

          expirationSeconds: 7200

          audience: vault

A projected volume enables us to mount into a single directory, volumes from several existing volume sources. The reason that we use a projected volume is that a pod can have different tokens for communication with different services in the cluster.

Conclusion

Service account token volume projection is a feature that builds over the mechanism of the service account. It allows inter-pod communications in a cluster, which is an important requirement of modern applications that primarily based on microservices architecture. This feature is designed as such that we can plugin external services such as Google to the Kubernetes cluster to consume their authentication system.

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