Multi-Tenancy in K8s & OpenShift #7 - Securing Persistent Storage Isolation

In this series, we've already covered Namespace-Based Isolation, Network Policies, RBAC, and Resource Quotas and LimitRanges to ensure secure, fair resource management in multi-tenant Kubernetes clusters. In the previous blog, we discussed Pod Security Standards (PSS) for Workload Security, which help enforce security best practices at the pod level, ensuring that tenants deploy only secure workloads in a multi-tenant environment.

In multi-tenant Kubernetes environments, ensuring isolated storage for tenants is crucial for both security and data integrity. Storage Isolation helps protect each tenant's data, preventing accidental or malicious access from other tenants. By implementing storage isolation practices for Persistent Volumes (PVs) and Persistent Volume Claims (PVCs), we can ensure persistent volume security and enable effective multi-tenancy in Kubernetes clusters.

Multi-Tenancy in Kubernetes & Openshift: A Comprehensive Guide

Part 1: Use Cases & Implementations

Part 2: Namespace-Based Isolation for Workload Separation

Part 3: Network Policies for Network Isolation

Part 4: Role-Based Access Control (RBAC) for Authorization

Part 5: Resource Quotas and LimitRanges for Resource Control

Part 6: Pod Security Standards (PSS) for Workload Security

Part 7: Storage Isolation for Persistent Volume Security

Part 8: Ingress Control Isolation for External Access Segregation

Part 9: Control Plane Robustness to Safeguard shared Kubernetes Resources

Part 10: NodePort and HostPort Restrictions for Enhanced Network Security

Part 11: Resource and Cost Tracking for ShowBack/ChargeBack

Part 12: Multi-Tenant Considerations for Shared Tools

Storage Isolation for Persistent Volume Security

What Is Storage Isolation in Kubernetes?

Storage isolation means that each tenant’s persistent storage is completely separate from others. Kubernetes uses Persistent Volumes (PVs) to provide durable storage and Persistent Volume Claims (PVCs) to request and use this storage within pods. In a multi-tenant environment, it's crucial that PVs and PVCs are isolated at the namespace or tenant level to prevent cross-tenant access to storage.

Why Is Storage Isolation Important for Multi-Tenancy?

In a multi-tenant setup, tenants often run workloads that require persistent storage. Without proper isolation, one tenant might inadvertently access, modify, or delete another tenant's data. Storage isolation helps ensure:

• Data Security: Tenants can't access each other's data, preventing unauthorized access and maintaining data privacy.

• Data Integrity: Proper isolation reduces the risk of accidental or intentional data corruption across tenants.

• Compliance: For environments requiring data security compliance, storage isolation makes sure that data is only accessible by authorized users within their specific tenant boundaries.

How Storage Isolation Works in Kubernetes

• Persistent Volume Claims (PVCs): A tenant requests storage by creating a PVC within their namespace. This PVC then binds to a suitable Persistent Volume (PV) that meets the requested storage requirements. Since PVCs are scoped to namespaces, they’re automatically isolated within the namespace.

• StorageClasses for Tenant-Specific Storage: A StorageClass defines how Kubernetes provisions storage. By using different StorageClasses for each tenant, you can ensure that PVs are provisioned on tenant-specific storage backends or storage types, providing stronger data separation.

• Dynamic Provisioning for On-Demand Storage: Kubernetes supports dynamic provisioning, which automatically creates PVs when PVCs are requested. By configuring dynamic provisioning per tenant, you can provide isolated storage for each tenant, with the correct level of security and access control.

Use Cases for Storage Isolation in Multi-Tenancy

• Dedicated Storage for Compliance: If certain tenants need to comply with data security regulations (e.g., GDPR, HIPAA), you can provision dedicated storage backends using StorageClasses to meet compliance requirements.

• Performance Isolation: By providing separate storage backends or classes per tenant, you ensure that one tenant’s storage operations don’t impact another tenant’s performance—especially useful in environments with high I/O demands.

• Data Security: When using shared storage infrastructure (like NFS or shared block storage), isolating tenants ensures that only their applications can access their specific data, maintaining privacy and security.

Best Practices for Storage Isolation

• Use Dedicated StorageClasses per Tenant: Configure separate StorageClasses for each tenant to ensure their data is isolated on different storage backends. This helps enforce security policies at the storage layer, providing stronger data separation.

• Apply VolumeBindingMode: WaitForFirstConsumer: This setting delays the binding of a Persistent Volume (PV) until a pod using the Persistent Volume Claim (PVC) is scheduled. This ensures PVs are only provisioned in response to specific tenant workloads, reducing the risk of accidental cross-tenant access.

• Implement Access Control on PVs and PVCs: While PVCs are scoped to namespaces, it’s also crucial to implement Role-Based Access Control (RBAC). This ensures only authorized tenants can create, modify, or delete PVCs within their namespace, maintaining control over who can access storage resources.

• Use Dynamic Provisioning: Enable dynamic provisioning to automatically create PVs for tenants based on their PVC requests. This minimizes manual intervention and ensures storage is provisioned in an isolated manner for each tenant.

Conclusion

In a multi-tenant Kubernetes environment, storage isolation is key to securing persistent volumes and ensuring data integrity. By utilizing tenant-specific StorageClasses, dynamic provisioning, and setting up Persistent Volumes with WaitForFirstConsumer, you can maintain secure and isolated storage environments for each tenant. These best practices are vital for protecting tenant data and ensuring compliance with data security requirements in a shared Kubernetes environment.

Simplifying Multi-Tenancy with Stakater Multi-Tenant Operator

Implementing multi-tenancy in Kubernetes can be a complex task. It requires a thorough understanding of Kubernetes and the configuration of multiple components, such as namespace isolation, network policies, RBAC, and resource quotas. Setting it up effectively takes time and effort to ensure both security and resource management are properly handled. This is where the Stakater Multi-Tenant Operator (MTO) shines.

The MTO is designed to simplify and accelerate the process of implementing multi-tenancy across Kubernetes clusters. It provides a robust, automated framework for managing tenants, enabling organizations to quickly establish secure, isolated, and well-managed environments.

When paired with storage isolation practices, the MTO enhances data security by ensuring each tenant’s persistent storage remains isolated. This is crucial in a multi-tenant environment to prevent unauthorized access and maintain data integrity. Features like dedicated StorageClasses and dynamic provisioning ensure each tenant’s storage is provisioned securely, strengthening the overall security posture of the Kubernetes environment.

In the next blog, we’ll dive into Ingress Control Isolation for External Access Segregation, exploring how to manage external access to services in a multi-tenant setup and ensure proper isolation of traffic between tenants.