As you adopt Kubernetes, you gain the flexibility to deploy, scale, and manage containerized applications in a highly available manner. But this new level of control and responsibility also comes with new security challenges.
Kubernetes is a complex system with many components and moving parts, making it difficult to secure by default. However, by following some simple best practices, you can harden your Kubernetes cluster and protect your applications from common threats.
In this article, we'll cover some of the most important Kubernetes security best practices, including:
Role-based access control (RBAC) is a Kubernetes feature that allows you to granularly control which users and service accounts have access to which Kubernetes resources.
RBAC is disabled by default in Kubernetes, so the first step to securing your cluster is to enable it. You can do this by passing the --authorization-mode=RBAC
flag to the kube-apiserver
binary when starting your Kubernetes cluster.
Once RBAC is enabled, you can create Role
and ClusterRole
objects to define the permissions that should be granted to a given user or service account. For example, you could create a Role
that allows a user to view and list all resources in a namespace, but not create or delete any resources.
You can then create a RoleBinding
or ClusterRoleBinding
to bind a Role
or ClusterRole
to a user or service account. This will grant the specified permissions to the user or service account.
It's important to note that, by default, any authenticated user will have full access to the Kubernetes API. This means that, unless you explicitly restrict access with RBAC, any user who can authenticate to your Kubernetes cluster will be able to perform any action, including deleting all resources in the cluster.
Transport Layer Security (TLS) is a protocol that allows you to encrypt network traffic to prevent eavesdropping and tampering.
Kubernetes uses TLS to encrypt all communication between components, as well as communication between the Kubernetes API server and clients. By default, Kubernetes will generate self-signed certificates for all components. While this is sufficient for most development and testing environments, you should use signed certificates in production to ensure that traffic cannot be intercepted or tampered with.
You can generate signed certificates using a certificate authority (CA) of your choice, or you can use a tool like kube-ssl
to automatically generate and deploy signed certificates for your Kubernetes cluster.
Network policy is a Kubernetes feature that allows you to control which pods are allowed to communicate with each other. By default, all pods in a Kubernetes cluster can communicate with each other, but this exposes your applications to unnecessary risk.
For example, if you have a pod that contains sensitive data, you may want to restrict communications to only allow communication from trusted pods. Or, if you have an application that consists of multiple microservices, you may want to restrict communications to only allow communication between the services that need to communicate with each other.
Network policy is implemented as a Kubernetes resource, and you can use it to specify which pods are allowed to communicate with each other. For example, the following network policy will allow communication between pods in the frontend
and backend
namespaces, but will not allow communication between pods in the frontend
namespace and pods in the database
namespace:
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
name: frontend-backend
namespace: frontend
spec:
podSelector:
matchLabels:
app: frontend
policyTypes:
- Ingress
- Egress
ingress:
- from:
- podSelector:
matchLabels:
app: backend
egress:
- to:
- podSelector:
matchLabels:
app: backend
Network policy is a complex topic, and there are many different ways to configure it. We recommend reading the Kubernetes documentation on network policy for more information.
A security context is a set of security-related options that can be applied to a pod or container. These options can be used to control things like which users and groups are allowed to access the pod or container, as well as which capabilities are allowed.
By default, containers in Kubernetes are run as the root
user, which gives the containers full access to the host system. This is a major security risk, as a malicious container could potentially access sensitive host system data or even take over the entire host system.
To mitigate this risk, you should always run containers in a least-privileged security context. This means specifying a non-root user for the container to run as, as well as specifying which capabilities the container is allowed to use.
For example, the following Pod
definition will run the nginx
container as the nginx
user and will not allow the container to use any capabilities:
apiVersion: v1
kind: Pod
metadata:
name: nginx
namespace: default
spec:
securityContext:
runAsUser: 1000
fsGroup: 1000
containers:
- name: nginx
image: nginx
securityContext:
capabilities: {}
Running containers as a non-root user is a good security practice in general, and is especially important in Kubernetes where containers can potentially access sensitive host system data.
The Kubernetes API server is the central point of communication for all Kubernetes components, and it is responsible for processing all API requests. This makes the API server a critical component of the Kubernetes system, and it is important to secure it to prevent unauthorized access.
One way to secure the API server is to use TLS certificates to encrypt all traffic to and from the API server. As we mentioned earlier, Kubernetes will generate self-signed certificates for all components by default, but you should use signed certificates in production to ensure that traffic cannot be intercepted or tampered with.
Another way to secure the API server is to use an authentication plugin. Kubernetes includes a number of built-in authentication plugins, including HTTPBasicAuth
, Token
, X509
, and Webhook
. You can also use third-party authentication plugins, such as OIDC
or LDAP
.
Image scanners are tools that help you enforce security policies for container images. For example, you can use an image scanner to check for known vulnerabilities in your images, or to enforce policies that require images to be signed by a trusted authority.
Kubernetes includes a built-in image scanner called Clair
, which can be used to scan images for known vulnerabilities. Clair is an open source project, and you can find more information about it on the project website.
In addition to Clair, there are a number of other image scanners available, both open source and commercial. We recommend doing some research to find an image scanner that meets your specific needs.
In this article, we've covered some of the most important Kubernetes security best practices. By following these best practices, you can harden your Kubernetes cluster and protect your applications from common threats.