Securely Deploying and Running Multiple Tenants on Kubernetes

Kubernetes has become the backbone of modern cloud native applications, and as adoption grows, organizations increasingly seek to consolidate workloads and resources by running multiple tenants within the same Kubernetes infrastructure. These tenants could be internal teams, or departments within a company that share a Kubernetes cluster for development and production. Alternatively, they could be external clients, which are SaaS providers hosting customer workloads on shared infrastructure.

While multitenancy offers cost efficiency and centralized management, it also introduces security and operational challenges. The three considerations users must take into account include:

• How do you ensure strong isolation between tenants?
• How do you manage resources and prevent one tenant from affecting another?
• How do you meet regulatory and compliance requirements?

To address these concerns, practitioners have three primary options for deploying multiple tenants securely on Kubernetes. Here, we will dive into the three options and outline the main considerations for each.

How to Deploy Multiple Tenants on Kubernetes

Namespace-Based Isolation with Network Policies, RBAC and Security Controls

Namespaces are Kubernetes’ built-in mechanism for logical isolation. This approach uses:

• Namespaces: Logical boundaries for separating tenant workloads.
• RBAC (Role-Based Access Control): Restricts tenant access to their namespace and resources.
• Network policies: Controls ingress and egress traffic between pods and namespaces.
• Resource quotas: Limits CPU, memory and other resources to prevent noisy neighbors.

Advantages include cost-effectiveness, as tenants share the cluster infrastructure. What’s more, this approach is simple to manage with centralized operations within a single cluster. Limitations include security risks if misconfigurations occur in RBAC or network policies.

Below is a deeper dive with additional considerations when it comes to the Namespace-Based Isolation approach.

• Isolation Level: Logical isolation using namespaces, RBAC and network policies. Relies on proper configuration.
• Security: Vulnerabilities in shared components (such as API server) or misconfigured policies can lead to breaches.
• Resource Contention: All tenants share cluster resources like nodes and control planes, leading to potential resource contention.
• Scalability: Adding new tenants requires creating a new namespace and applying policies within the existing cluster.
• Cost: Shared cluster resources reduce infrastructure and operational costs.
• Operational Complexity: Single cluster to manage, but requires careful configuration of namespaces, RBAC and network policies.
• Performance Isolation: Tenants share control plane and node resources, potentially affecting performance during resource spikes.
• Management Overhead: Centralized control over tenants within one cluster.

Cluster-Level Isolation

The cluster-level isolation approach assigns each tenant a dedicated Kubernetes cluster, ensuring complete physical or virtual isolation. Tools like Rancher, Google Anthos and AWS EKS simplify managing multiple clusters.

Advantages of this approach include strong isolation, as tenants do not share any cluster components. The levels of security are also high, with no risk of cross-tenant data leakage or resource contention. 

Limitations exist, however, such as high cost: each cluster incurs control plane and node costs. Additional limitations include operational complexity and scalability challenges. Managing, upgrading and monitoring multiple clusters is resource-intensive, and provisioning new clusters can delay tenant onboarding.

Here are more details and considerations with regard to the Cluster-Level Isolation approach.

• Isolation Level: Physical or virtual isolation; no shared cluster components.
• Security: High security, as one tenant’s vulnerabilities do not affect others.
• Resource Contention: Dedicated resources for each tenant ensure no resource interference or contention.
• Scalability: Adding new tenants requires provisioning and managing new clusters, making scalability limited.
• Cost: Separate clusters increase infrastructure, operational and monitoring costs.
• Operational Complexity: Managing multiple clusters adds significant operational overhead and requires specialized tools.
• Performance Isolation: Performance is isolated due to dedicated clusters.
• Management Overhead: Separate control planes and clusters increase management overhead.

Virtual Clusters

Virtual clusters provide tenant-specific control planes within a shared physical cluster. Each tenant gets their virtual Kubernetes environment while sharing the worker nodes and physical infrastructure.

Advantages include strong logical isolation, meaning that tenant workloads operate independently. This approach is also cost efficient, as shared worker nodes reduce infrastructure costs. Another advantage is scalability, as virtual clusters can be provisioned quickly–often in seconds.

Limitations include higher complexity due to infrastructure-level isolation compared to namespace-based isolation, and performance impact if worker nodes are over-committed.

The list below includes additional considerations with the Virtual Clusters approach.

Virtual Clusters

• Isolation Level: Each tenant gets a virtual Kubernetes cluster running inside a shared physical cluster.
• Security: Virtual clusters provide tenant-specific control planes, reducing risk of cross-tenant issues.
• Resource Contention: Shared worker nodes but isolated control planes reduce contention for control-plane-related operations.
• Scalability: New virtual clusters can be provisioned quickly within the existing physical cluster.
• Cost: Shared infrastructure reduces costs compared to physical clusters but higher than namespace isolation.
• Operational Complexity: Centralized management simplifies operations compared to physical clusters, but still involves managing virtual clusters.
• Performance Isolation: Control planes are isolated; however, shared worker nodes affect performance.
• Management Overhead: Simplified management compared to physical clusters but more overhead than namespaces.

What Are the Implications of Leaving Multitenancy Unaddressed?

Implementing a robust multitenancy strategy is critical. Failing to do so can lead to devastating consequences in terms of security, compliance, and operational inefficiencies. Specific issues include:

• Security breaches: Misconfigurations in shared clusters can allow one tenant to access another’s workloads or data.
• Resource contention: A single tenant can monopolize shared resources, degrading performance for others.
• Non-compliance: Inadequate isolation can result in failure to meet regulatory requirements like HIPAA or PCI-DSS.
• Operational inefficiency: Poorly designed multitenancy increases management overhead and risks cluster downtime.

Secure multitenancy in Kubernetes is essential for maintaining the security posture of Kubernetes clusters for compliance and security requirements. Multitenancy consolidates workloads and resources efficiently and saves money with centralized management, but introduces significant security and operational challenges that must be addressed through best practices such as namespace-based isolation or secure deployment of virtual clusters. 

Failing to properly secure multitenancy can lead to compliance violations and security gaps, making implementing robust security measures and isolation techniques paramount for maintaining a secure and efficient multitenant environment in Kubernetes.

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Author Bio

Ratan Tipirneni is President & CEO at Tigera, where he is responsible for defining strategy, leading execution, and scaling revenues. Ratan is an entrepreneurial executive with extensive experience incubating, building, and scaling software businesses from early stage to hundreds of millions of dollars in revenue. He is a proven leader with a track record of building world-class teams.

 

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