Kubernetes Security: 8 Best Practices to Secure Your Cluster

Kubernetes is an open-source platform designed for managing containerized workloads and services. It offers a range of features that make it easier for organizations to deploy and manage complex applications. However, as with any technology, security is a critical concern when using Kubernetes.

In this blog post, we will discuss the best practices for securing Kubernetes to ensure that your deployments are safe from attacks and other security issues.

1. Use Role-Based Access Control (RBAC)

Kubernetes comes with built-in RBAC, which provides a granular level of access control. With RBAC, you can define what resources a user can access and what operations they can perform. By using RBAC, you can limit access to the Kubernetes API and ensure that only authorized users can manage your cluster.

Role-Based Access Control (RBAC) is a security mechanism in Kubernetes that allows cluster administrators to control access to resources based on user roles and permissions. RBAC provides a granular level of access control, which makes it possible to define what resources a user can access and what operations they can perform within the cluster.

To understand how RBAC works in Kubernetes, let’s consider an example. Suppose you have a Kubernetes cluster with two namespaces: “production” and “development.” You want to define a set of permissions for users in each namespace to ensure that they can only access the resources they need to do their job.

First, you will need to define a role for each namespace. A role is a set of permissions that define what actions a user can perform on a particular resource. For example, you can create a role called “developer” for the “development” namespace that allows users to create and delete pods, but does not allow them to access secrets or config maps.

Once you have defined the roles, you can create a role binding. A role binding associates a role with one or more users or groups. For example, you can create a role binding that associates the “developer” role with a group of developers who need access to the “development” namespace.

Finally, you can test the RBAC configuration by trying to perform an action that requires a certain level of access. For example, if a user tries to access a resource in the “production” namespace without the necessary permissions, they will receive an error message.

Here is an example YAML file that defines a role and a role binding for the “development” namespace:

apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  name: developer
  namespace: development
rules:
- apiGroups: [""]
  resources: ["pods"]
  verbs: ["create", "delete"]

---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  name: dev-group
  namespace: development
subjects:
- kind: Group
  name: developers
  apiGroup: rbac.authorization.k8s.io
roleRef:
  kind: Role
  name: developer
  apiGroup: rbac.authorization.k8s.io

In this example, the “developer” role allows users to create and delete pods in the “development” namespace. The “dev-group” role binding associates the “developer” role with the “developers” group, which contains the users who need access to the “development” namespace.

By using RBAC, you can ensure that users only have access to the resources they need, which minimizes the risk of security issues caused by human error or malicious actors. RBAC is a powerful security mechanism that can help organizations control access to their Kubernetes clusters and protect against unauthorized access and data breaches.

2. Enable Network Policies

Kubernetes network policies are used to control the traffic flow between pods and other network resources. Network policies can help prevent unauthorized access and protect against network-based attacks. By enabling network policies, you can restrict network traffic between different namespaces or pods, based on specific rules.

Kubernetes Network Policies are a powerful tool for securing communication between pods in a Kubernetes cluster. Network Policies enable you to define rules for traffic flow within a cluster, which can be used to isolate workloads and prevent unauthorized access to sensitive data.

To enable Network Policies in your Kubernetes cluster, you must first ensure that your cluster’s network plugin supports the Network Policy API. The most popular network plugins that support Network Policies include Calico, Cilium, and Weave Net.

Once you have verified that your network plugin supports Network Policies, you can start creating policies. Here is an example of how to create a Network Policy that allows traffic only between pods in the same namespace:

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-same-namespace
spec:
  podSelector: {}
  policyTypes:
  - Ingress
  ingress:
  - from:
    - podSelector: {}

In this example, the “allow-same-namespace” Network Policy allows all traffic (Ingress) from any pod within the same namespace. The podSelector field is set to an empty object, which matches all pods in the namespace. This policy ensures that only pods within the same namespace can communicate with each other.

Here is another example of a Network Policy that allows traffic only between pods with specific labels:

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-specific-pods
spec:
  podSelector: {}
  policyTypes:
  - Ingress
  ingress:
  - from:
    - podSelector:
        matchLabels:
          app: web

In this example, the “allow-specific-pods” Network Policy allows all traffic (Ingress) from any pod with the label “app: web”. This policy ensures that only pods with the label “app: web” can communicate with each other.

You can also create more complex policies that allow or block traffic based on a combination of source IP address, port, and protocol. Here is an example of a Network Policy that blocks all traffic to a specific pod:

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: block-specific-pod
spec:
  podSelector:
    matchLabels:
      app: db
  policyTypes:
  - Ingress
  ingress:
  - from:
    - ipBlock:
        cidr: 192.168.0.0/16

In this example, the “block-specific-pod” Network Policy blocks all traffic (Ingress) to any pod with the label “app: db”. The from field is set to an ipBlock that matches the CIDR range 192.168.0.0/16, which blocks traffic from any IP address in that range.

By creating Network Policies in your Kubernetes cluster, you can enforce security rules that restrict traffic flow between pods and ensure that your workloads are isolated and protected. Network Policies are a powerful tool for securing communication within a cluster and can help you minimize the risk of unauthorized access and data breaches.

3. Use Secrets Management

Kubernetes allows you to store sensitive information, such as API keys, passwords, and certificates, in the form of secrets. Secrets can be mounted into pods, and they are encrypted at rest. By using secrets management, you can avoid storing sensitive data in plain text and minimize the risk of unauthorized access.

Secrets are sensitive pieces of information, such as passwords, API keys, and TLS certificates, that are used by applications to authenticate and secure communication. Managing secrets securely is crucial to maintaining the security and integrity of your applications and data. Kubernetes provides a built-in Secrets API that enables you to manage secrets and securely inject them into your applications.

To create a secret, you can use the kubectl command-line tool to generate the secret or create it manually in a YAML file. Here is an example of creating a secret using kubectl:

$ kubectl create secret generic my-secret \
    --from-literal=username=my-username \
    --from-literal=password=my-password

In this example, the kubectl create secret command creates a generic secret named my-secret and populates it with two key-value pairs: username=my-username and password=my-password. The –from-literal flag indicates that the values are specified directly on the command line.

Once you have created a secret, you can use it in your application by referencing it in a Kubernetes manifest file. Here is an example of how to use a secret in a deployment:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-app
spec:
  replicas: 1
  selector:
    matchLabels:
      app: my-app
  template:
    metadata:
      labels:
        app: my-app
    spec:
      containers:
        - name: my-container
          image: my-image
          env:
            - name: MY_USERNAME
              valueFrom:
                secretKeyRef:
                  name: my-secret
                  key: username
            - name: MY_PASSWORD
              valueFrom:
                secretKeyRef:
                  name: my-secret
                  key: password

In this example, the deployment includes two environment variables, MY_USERNAME and MY_PASSWORD, which are populated with the values from the my-secret secret. The valueFrom field specifies that the values should be fetched from the my-secret secret using the secretKeyRef object, which references the key names in the secret.

You can also mount a secret as a volume in a pod. Here is an example of how to mount a secret as a volume in a pod:

apiVersion: v1
kind: Pod
metadata:
  name: my-pod
spec:
  containers:
    - name: my-container
      image: my-image
      volumeMounts:
        - name: my-secret-volume
          mountPath: /etc/my-secret
          readOnly: true
  volumes:
    - name: my-secret-volume
      secret:
        secretName: my-secret

In this example, the pod includes a volume named my-secret-volume that is mounted at the path /etc/my-secret in the container. The secretName field in the secret object specifies the name of the secret to mount.

By using Kubernetes Secrets, you can manage and securely inject sensitive information into your applications without exposing them in plain text in your deployment manifests. Secrets enable you to keep your applications secure and compliant with regulatory requirements. With proper secrets management, you can minimize the risk of data breaches and ensure that your applications and data are protected.

4. Enable Pod Security Policies

Pod security policies (PSPs) can be used to enforce security controls at the pod level. PSPs define what actions a pod can perform, such as which host namespaces and devices it can access. By enabling PSPs, you can prevent attackers from using compromised pods to gain access to your cluster.

Pod Security Policies (PSP) are a Kubernetes feature that allows cluster administrators to enforce security policies that restrict the types of containers and the privileges they can run with. PSP can be used to mitigate common container vulnerabilities and reduce the attack surface of a Kubernetes cluster.

To enable PSP, you first need to create a policy that specifies the security requirements for pods in the cluster. Here is an example of a PSP that restricts the use of privileged containers:

apiVersion: policy/v1beta1
kind: PodSecurityPolicy
metadata:
  name: restricted
spec:
  privileged: false
  seLinux:
    rule: RunAsAny
  runAsUser:
    rule: RunAsAny
  fsGroup:
    rule: RunAsAny
  volumes:
  - configMap
  - secret
  - emptyDir
  - projected
  - downwardAPI

In this example, the PSP named restricted disallows the use of privileged containers and allows only certain types of volumes to be used in pods.

After creating the policy, you need to create a ClusterRole that specifies which users or groups are allowed to use the policy. Here is an example of a ClusterRole that allows the use of the restricted PSP:

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: restricted
rules:
- apiGroups:
  - policy
  resources:
  - podsecuritypolicies
  resourceNames:
  - restricted
  verbs:
  - use

In this example, the ClusterRole named restricted allows users or groups to use the restricted PSP to create pods.

Finally, you need to create a ClusterRoleBinding that binds the ClusterRole to the users or groups that should be allowed to use the policy. Here is an example of a ClusterRoleBinding that allows the default service account to use the restricted PSP:

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: restricted
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: restricted
subjects:
- kind: ServiceAccount
  name: default
  namespace: my-namespace

In this example, the ClusterRoleBinding named restricted allows the default service account in the my-namespace namespace to use the restricted PSP.

With PSP enabled, any attempt to create a pod that does not comply with the policy will be rejected. This helps ensure that only authorized users or groups can create pods with the required level of security. By using PSP, you can help secure your Kubernetes cluster and minimize the risk of container-based attacks.

5. Implement Image Scanning

Kubernetes allows you to scan container images for vulnerabilities before they are deployed. Image scanning can help identify known vulnerabilities and reduce the risk of running containers with known security issues. By integrating image scanning into your build pipeline, you can ensure that only secure container images are deployed.

Implementing image scanning is an important step in securing your Kubernetes cluster. Image scanning helps identify vulnerabilities and risks in container images before they are deployed in production, reducing the attack surface and minimizing the risk of exploits.

One way to implement image scanning is by using a container image scanning tool. These tools scan container images for known vulnerabilities, configuration issues, and other security risks. One popular tool is Clair, an open-source vulnerability scanner that can be integrated with Kubernetes.

Here’s an example of how to implement image scanning with Clair:

• Install Clair: First, you need to install and configure Clair. Clair consists of two components: a server and a client. The server runs as a Kubernetes deployment, while the client is used to scan container images. You can install Clair using a Kubernetes manifest file, or you can use a Helm chart for easier installation.
• Integrate Clair with your registry: Next, you need to integrate Clair with your container registry. This allows Clair to automatically scan container images as they are pushed to the registry. To integrate Clair with your registry, you need to configure the registry to send notifications to Clair when a new image is pushed. This can be done using a webhook or a notification system like Google Cloud Pub/Sub.
• Scan images: Once Clair is installed and integrated with your registry, you can start scanning container images. You can scan images manually using the Clair client, or you can configure Clair to automatically scan images as they are pushed to the registry. When a vulnerability is detected, Clair will return a report that lists the vulnerabilities and their severity levels.

Here’s an example of how to scan an image using the Clair client:

$ docker pull nginx:latest
$ sudo docker save nginx:latest | clairctl analyze --report nginx.json

In this example, we pull the latest version of the nginx container image, then save it as a file and analyze it using the Clair client. The –report option specifies the name of the output file that contains the vulnerability report.

• Automate scanning with Kubernetes admission controller: Finally, you can automate image scanning using a Kubernetes admission controller. This allows you to reject container images that fail the scanning process, ensuring that only secure images are deployed in your cluster. To automate scanning, you need to create a Kubernetes admission controller that invokes Clair when a new image is pushed to the registry. The controller can be implemented using a webhook or a Kubernetes API server extension. Here’s an example of how to implement an admission controller with Clair:

apiVersion: admissionregistration.k8s.io/v1
kind: ValidatingWebhookConfiguration
metadata:
  name: image-validation-webhook
webhooks:
- name: image-validation.example.com
  rules:
  - apiGroups: [""]
    apiVersions: ["v1"]
    resources: ["pods"]
    operations: ["CREATE"]
  clientConfig:
    service:
      name: clair
      namespace: clair
      path: /validate

In this example, we create a validating webhook that invokes Clair when a new pod is created. The webhook sends a request to the Clair service in the clair namespace with the path /validate. If the image fails the scanning process, the webhook rejects the pod creation request.

By implementing image scanning with a tool like Clair, you can improve the security of your Kubernetes cluster and minimize the risk of container-based attacks. Scanning container images for vulnerabilities and security risks is an essential part of any Kubernetes security strategy.

6. Use a Secure Container Registry

When deploying containerized applications, you will need to use a container registry to store and manage your images. It’s essential to use a secure container registry to protect against unauthorized access and image tampering. By using a container registry with built-in security features, such as image signing and access controls, you can minimize the risk of security issues.

A secure container registry is a critical component of a secure Kubernetes environment. A container registry is a service that stores and distributes container images. It is where your organization’s container images are stored, and it should be properly secured to prevent unauthorized access to sensitive data and code.

Here’s an example of how to use a secure container registry:

• Choose a secure registry: There are several secure container registry options available, including public cloud offerings like Google Container Registry and private options like Harbor. When choosing a registry, consider the level of security required, the cost, and the ease of integration with your existing toolchain.
• Secure access to the registry: Once you’ve chosen a secure registry, you need to secure access to it. You can do this by configuring access controls and authentication mechanisms to ensure that only authorized users can access the registry.
• Use encryption: Encryption can help secure your registry data in transit and at rest. Use SSL/TLS encryption to protect data in transit and implement disk encryption to protect data at rest.
• Enable logging and monitoring: Enable logging and monitoring for your container registry to detect and respond to security threats quickly. Monitor access logs for unusual activity, and use tools like Kubernetes security dashboards and alerting systems to stay on top of security events.
• Scan container images for vulnerabilities: As mentioned in a previous answer, it’s important to scan container images for vulnerabilities before deploying them in production. You can integrate your secure container registry with a container scanning tool like Clair to scan container images automatically for vulnerabilities.

Here’s an example of how to use Google Container Registry as a secure container registry:

• Create a GCR repository: To create a repository in Google Container Registry, use the gcloud command-line tool. For example, the following command creates a repository named my-repo in the us-west1 region:

$ gcloud beta container repositories create my-repo --region=us-west1

• Authenticate with GCR: To authenticate with Google Container Registry, use the gcloud auth configure-docker command. This command configures Docker to use your GCP credentials to authenticate with GCR.

$ gcloud auth configure-docker

• Push an image to GCR: To push a Docker image to Google Container Registry, use the docker push command. For example, the following command pushes an image named my-image to the my-repo repository:

$ docker tag my-image gcr.io/my-project/my-repo/my-image
$ docker push gcr.io/my-project/my-repo/my-image

• Configure access controls: You can configure access controls for your GCR repository using IAM roles. For example, the following command grants the storage.buckets.get permission to a service account named my-service-account:

$ gcloud projects add-iam-policy-binding my-project \
  --member serviceAccount:my-service-account@my-project.iam.gserviceaccount.com \
  --role roles/storage.buckets.get

By using a secure container registry like Google Container Registry and following best practices for securing access and data, you can help ensure the security of your Kubernetes environment.

7. Regularly Update and Patch

Kubernetes is a rapidly evolving technology, with new features and bug fixes being released regularly. It’s essential to keep your Kubernetes clusters up to date to ensure that you are benefiting from the latest security enhancements. Additionally, you should regularly check for any security patches and apply them as soon as possible.

Regularly updating and patching your Kubernetes environment is crucial for keeping it secure. As with any software, Kubernetes and its components can have vulnerabilities that can be exploited by attackers. When vulnerabilities are discovered, the Kubernetes community releases patches to fix them. To ensure that your Kubernetes environment remains secure, it’s important to regularly apply these patches and updates.

Here’s an example of how to regularly update and patch your Kubernetes environment:

• Stay informed about vulnerabilities: Keep track of the latest vulnerabilities and patches for Kubernetes and its components. Subscribe to security newsletters and announcements, and follow the Kubernetes community and relevant security organizations on social media. Regularly check the Kubernetes CVE database to stay up-to-date on the latest vulnerabilities.
• Plan and schedule updates: Plan and schedule updates to your Kubernetes environment based on the level of risk and impact on your organization. Make sure to test updates on a non-production environment before applying them to production.
• Update Kubernetes components: To update Kubernetes components, you can use tools like kubeadm, kops, or kubespray. For example, to upgrade a cluster using kubeadm, you can use the following command:

$ kubeadm upgrade apply v1.22.2

• Update container images: Regularly update the container images used in your Kubernetes environment to ensure that you’re using the latest and most secure versions. You can use tools like Kubernetes Deployment and StatefulSet to manage and update container images.
• Review and validate updates: After applying updates, review and validate your Kubernetes environment to ensure that everything is working as expected. Check that all applications are still running, and monitor the environment for any unusual behavior.
• Rollback if necessary: If an update causes issues or unexpected behavior, roll back to the previous version. Make sure to have a rollback plan in place before applying updates.

Regularly updating and patching your Kubernetes environment is a critical step in keeping it secure. By staying informed about the latest vulnerabilities and updates, planning and scheduling updates, and testing and validating updates before applying them to production, you can help ensure that your Kubernetes environment remains secure.

8. Use a Kubernetes-Specific Firewall

A firewall can be used to filter network traffic and protect your Kubernetes clusters from external attacks. However, traditional firewalls may not be suitable for Kubernetes because they may not be aware of the unique Kubernetes network architecture. A Kubernetes-specific firewall, such as Calico, can be used to secure your cluster and ensure that only authorized traffic is allowed.

A Kubernetes-specific firewall is a network security solution that is designed specifically for use with Kubernetes clusters. It provides additional security by restricting network traffic to and from Kubernetes pods and nodes.

Here’s an example of how to use a Kubernetes-specific firewall:

• Choose a firewall solution: There are several Kubernetes-specific firewall solutions available, including Calico, Flannel, and Cilium. Choose a solution that meets your security requirements and is compatible with your Kubernetes environment.
• Install the firewall solution: Install the chosen firewall solution on your Kubernetes cluster using the installation instructions provided by the vendor. This typically involves installing a DaemonSet that runs the firewall software on each node in the cluster.
• Configure network policies: Configure network policies using the firewall solution’s configuration language. Network policies define the rules for allowing or blocking traffic to and from Kubernetes pods and nodes.

For example, to allow traffic to a specific pod, you can create a network policy that allows traffic to the pod’s IP address and port:

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-web-traffic
spec:
  podSelector:
    matchLabels:
      app: web
  ingress:
  - from:
    - ipBlock:
        cidr: 10.0.0.0/16
    ports:
    - port: 80
      protocol: TCP

This network policy allows traffic from the 10.0.0.0/16 CIDR block to the pod labeled “app=web” on port 80.

• Test and validate network policies: Test and validate network policies to ensure that they are working as expected. You can use tools like kubectl and tcpdump to test network policies.
• Monitor network traffic: Monitor network traffic to detect any unauthorized or unusual activity. Use tools like Prometheus and Grafana to monitor network traffic and alert on suspicious activity.
• By using a Kubernetes-specific firewall, you can add an extra layer of security to your Kubernetes environment. By configuring network policies that allow or block traffic to and from pods and nodes, you can help protect your Kubernetes cluster from unauthorized access and malicious activity.

9. Use Network Encryption

Kubernetes supports network encryption using Transport Layer Security (TLS). By enabling network encryption, you can protect against man-in-the-middle attacks and ensure that data transmitted between pods and other network resources is secure. Additionally, you should configure your Kubernetes API server to use a secure connection.

Network encryption is the process of encrypting network traffic to protect it from unauthorized access or interception. In a Kubernetes environment, network encryption can be used to secure communication between pods, nodes, and other components.

Here’s an example of how to use network encryption in a Kubernetes environment:

• Choose a network encryption solution: There are several network encryption solutions available for use with Kubernetes, including Transport Layer Security (TLS) and Virtual Private Networks (VPNs). Choose a solution that meets your security requirements and is compatible with your Kubernetes environment.
• Generate TLS certificates: If using TLS encryption, generate TLS certificates for the Kubernetes components that will communicate with each other. These certificates are used to authenticate the identity of the components and encrypt communication between them.
• Configure encryption for communication between components: Configure network encryption for communication between Kubernetes components using the chosen solution. For example, to use TLS encryption with the Kubernetes API server, you can add the following flag to the API server’s configuration file:

--tls-cert-file=/path/to/tls.cert
--tls-private-key-file=/path/to/tls.key

This tells the API server to use the TLS certificate and private key when encrypting communication.

• Configure encryption for communication between pods: Configure network encryption for communication between pods using the chosen solution. For example, to use TLS encryption between pods in a Kubernetes cluster, you can use the NetworkPolicy API to enforce encrypted traffic:

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-tls-traffic
spec:
  podSelector: {}
  ingress:
  - from:
    - namespaceSelector:
        matchLabels:
          name: ns-1
    ports:
    - port: 443
      protocol: TCP
    tls:
      hosts:
      - api.example.com

This NetworkPolicy allows encrypted traffic from pods in the “ns-1” namespace to pods in any namespace on port 443 with a TLS hostname of “api.example.com”.

• Test and validate network encryption: Test and validate network encryption to ensure that it is working as expected. Use tools like Wireshark to capture and analyze network traffic to verify that it is encrypted.

By using network encryption in your Kubernetes environment, you can help protect your network traffic from unauthorized access and interception. By configuring network encryption for communication between Kubernetes components and pods, you can add an extra layer of security to your Kubernetes environment.

10. Implement Runtime Security

Runtime security involves monitoring your Kubernetes clusters for suspicious activity and anomalies. By implementing runtime security, you can detect and respond to security incidents in real-time, before they cause significant damage. Runtime security can involve using tools such as intrusion detection systems (IDS) and security information and event management (SIEM) platforms.

Implementing runtime security in a Kubernetes environment is critical for detecting and preventing security threats at runtime. Here’s an example of how to implement runtime security in a Kubernetes environment:

• Choose a runtime security solution: There are several runtime security solutions available for use with Kubernetes, including Falco, Aqua Security, and Sysdig. Choose a solution that meets your security requirements and is compatible with your Kubernetes environment.
• Install the runtime security solution: Install the chosen runtime security solution on your Kubernetes cluster using the installation instructions provided by the vendor. This typically involves installing a DaemonSet that runs the runtime security software on each node in the cluster.
• Configure runtime security policies: Configure runtime security policies using the security solution’s configuration language. Runtime security policies define the rules for detecting and preventing security threats at runtime.

For example, to detect a process running as root inside a container, you can create a runtime security policy that alerts when a container runs a process with a user ID of 0:

- rule: Detect process running as root
  desc: A process running as root inside a container
  condition: container.user.id = 0
  output: Process running as root (user=%container.user.name command=%proc.cmdline)
  priority: WARNING

This policy generates a warning when a container runs a process with a user ID of 0, indicating that it may be running as root.

• Test and validate runtime security policies: Test and validate runtime security policies to ensure that they are working as expected. Use tools like kubectl and Falco’s event viewer to test policies and verify that they generate alerts when security threats are detected.
• Monitor and respond to alerts: Monitor runtime security alerts to detect and respond to security threats at runtime. Use tools like Prometheus and Grafana to monitor alert volume and severity and configure alert notifications to be sent to a designated security team.

By implementing runtime security in your Kubernetes environment, you can help detect and prevent security threats at runtime. By configuring runtime security policies that detect security threats like process running as root and suspicious network traffic, you can add an extra layer of security to your Kubernetes environment.