Have you ever needed to serve multiple customers with a single instance of your application but ran into challenges like isolating each customer's data and configuration? If you have, then you've encountered a multi-tenant architecture.
In this blog post, we'll introduce the core concepts behind multi-tenancy and explore how it works. We'll then dive into how Kubernetes, the popular container orchestration platform, provides primitives that enable building multi-tenant architectures.
Finally, we'll highlight a few powerful open-source tools that can simplify your adoption of multi-tenancy on Kubernetes.
What is Multi-Tenancy?
Multi-tenancy is a practice of running multiple workloads in isolation from one another while sharing the same underlying resources. By enabling various tenants to coexist on the same infrastructure, multi-tenancy helps optimize resource utilization and reduces costs.
Multi-tenancy is categorized into two levels: "hard" and "soft" multi-tenancy. The Kubernetes documentation suggests that the distinction between them is not always clear-cut:
"The terms 'hard' and 'soft' can often be confusing, as no single definition will apply to all users. Instead, 'hardness' or 'softness' is better understood as a broad spectrum, with many different techniques that can be used to maintain different types of isolation in your clusters, based on your requirements."
In essence, hard and soft multi-tenancy represent different points on a spectrum of isolation techniques. The choice between them depends on your environment's specific requirements and constraints. To give you a clearer picture of the difference between the two:
Aspect | Hard Multi-Tenancy | Soft Multi-Tenancy |
---|---|---|
Isolation | Strong isolation between tenants, typically using separate clusters or virtual machines | In weaker isolation, tenants share the same cluster and underlying resources |
Security | Higher security due to stronger isolation | Lower security due to shared infrastructure |
Resource Efficiency | Lower resource efficiency due to dedicated resources for each tenant | Higher resource efficiency through shared resources |
Complexity | Higher complexity in management and maintenance | Lower complexity, easier to manage and maintain |
Cost | Higher cost due to dedicated infrastructure for each tenant | Lower cost due to shared infrastructure |
From the table above, hard multi-tenancy prioritizes strong isolation and security at the cost of resource efficiency and complexity. Soft multi-tenancy, on the other hand, offers better resource utilization and simplicity but with weaker isolation between tenants.
Use Cases for Multi-Tenancy on Kubernetes
To give you a better idea of how kubernetes can be leveraged for multi-tenant environments, let's explore a few use cases:
Use Case | Description |
---|---|
Teams | In many organizations, multiple teams often need to run their applications within the same Kubernetes cluster. Using the feature Kubernetes ships with, infrastructure teams can ensure each team has its own isolated environment within the shared cluster. |
SaaS Applications |
Another compelling use case for multi-tenancy in Kubernetes is running multiple instances of a Software as a Service (SaaS) application. In this scenario, each customer gets their own dedicated instance of the application, ensuring data isolation.
Imagine you are building a SaaS application that provides customer relationship management (CRM) functionality. With Kubernetes' multi-tenancy capabilities, you can deploy separate instances of your CRM application for each customer within the same cluster. Each instance runs in its own isolated environment with its database, configurations, and resources. This allows you to provide a personalized experience for each customer. |
Service Providers |
Multi-tenancy is a fundamental concept for many service providers, such as platform-as-a-service (PaaS) offerings like Vercel and Heroku. These platforms leverage multi-tenancy to support multiple users and applications running on the same underlying infrastructure.
By isolating each user's environment and resources, service providers can offer scalable and cost-effective solutions to their customers. While multi-tenancy is not exclusively tied to Kubernetes, it has become popular for service providers due to its robust isolation mechanisms and flexibility. PaaS/SaaS is a particularly interesting use case for multi-tenancy on Kubernetes. The Kubernetes API enables you to programmatically create new instances of an application, making it well-suited for building multi-tenant platforms. With just a few API calls, you can spin up a pod running an image of your choosing. When combined with a few other primitives, teams can quickly build out automated provisioning and management workflows. This means that when a new customer signs up for your service, you can instantly create a dedicated instance of your application tailored to their specific needs and requirements. |
How Kubernetes Enables Multi-Tenancy
So far, we have discussed what multi-tenancy is and some of the use cases in which Kubernetes can be leveraged to achieve a multi-tenant environment. Let's explore some of the built-in Kubernetes resources that can be used for setting this up.
Namespaces
This is where everyone starts when organizing services within their cluster. Namespaces provide a logical means for organizing resources. They allow you to group related resources collectively and apply policies and constraints to them. However, it's important to note that namespaces do not provide true isolation, as services can still communicate by default, and services within different namespaces can still communicate. This is because Kubernetes' default network policy allows all ingress and egress traffic between pods and services, regardless of their namespaces. Or, as Daniel Polenic put it, “Namespaces do not exist”
You'll need to combine them with network policies or a service mesh to achieve stronger isolation between namespaces. Leveraging a service mesh, such as Istio or Linkerd, can provide an additional layer of isolation and control over inter-service communication. Service meshes allow you to enforce fine-grained traffic policies and encrypt communication between services.
Network Policies
Network policies allow you to define ingress and egress rules. Ingress refers to incoming traffic to a resource, while egress refers to outgoing traffic from a resource. By leveraging network policies, you can govern service communication across namespaces and even your entire cluster.
For example, you can create a network policy that only allows services in the "payments" namespace to talk to the database deployed within the same cluster. While this is a significant improvement over using namespaces alone, it doesn't address the issue of resource consumption. What's to stop another service from using up all the resources on a node? This brings us to our next section, resources.
Resource Quotas and Limit Ranges
Resource quotas and limit ranges provide a way to control resource consumption within a namespace. Resource quotas allow you to set limits on the total amount of resources, CPU, and memory that can be consumed by all the pods within a namespace.
On the other hand, limit ranges allow you to define minimum and maximum resource constraints for individual pods within a namespace. This helps prevent resource starvation and ensures fair allocation of resources among pods.
To illustrate this visually, here's a diagram that provides a quick overview of how these resources work together to enable multi-tenancy in a Kubernetes cluster:
The Kubernetes cluster is divided into two namespaces in the diagram above, each representing a separate tenant. Within each namespace, we have the following resources:
Network Policies (represented in the blue rectangles) control traffic between resources within a namespace and across namespaces. In the diagram, Network Policy A1 in Namespace A allows traffic between certain resources, while Network Policy B1 in Namespace B restricts traffic.
Resource Quotas (represented in the orange rectangles) limit the total amount of resources (CPU and memory) that all the pods within a namespace can consume. Each namespace has its own resource quota defined, ensuring a fair allocation of resources among tenants.
Limit Ranges define the minimum and maximum resource limits for individual pods within a namespace. They help prevent resource starvation and ensure that pods are allocated resources within a specified range.
Benefits of Multi-Tenancy
So far, we've discussed the how and why of multi-tenancy. If you are still on the fence, here are some more concrete benefits.
Cost Savings
Using a single cluster with multiple tenants can lead to significant cost savings, especially if you aren't fully utilizing all your computing resources. By consolidating workloads from different teams or customers onto a shared cluster, you can optimize resource utilization and reduce the overall infrastructure costs.
Operational Simplicity
Managing a single, shared cluster is often simpler than dealing with multiple clusters or virtual machines (VMs) for each tenant. With a multi-tenant setup, you can apply similar manifests and configurations to onboard new tenants, streamlining the process.
Improved Scalability
Multi-tenancy in Kubernetes enables you to scale your applications and services more efficiently. You can easily allocate additional resources to specific tenants as your workloads grow without provisioning new clusters or VMs.
Built-in features, such as Horizontal Pod Autoscaling (HPA) and cluster autoscaling, allow you to automatically adjust the number of replicas and nodes based on the demand. With multi-tenancy, you can apply these scaling mechanisms at the tenant level, ensuring that each tenant's workload can scale independently without affecting others.
Open-Source Tools for Multi-Tenancy
While using Kubernetes primitives like namespaces, network policies, and resource quotas can help to keep things simple, sometimes you may require more robust isolation for your multi-tenant environments. Fortunately, there are open-source tools available to help with this.
- Kamaji: developed by Clastix, introduces the concept of hosted control planes. It allows you to create and manage multiple Kubernetes control planes within a single Kubernetes cluster. Each control plane operates independently, with its own set of API servers, controllers, and schedulers. This provides a higher level of isolation and autonomy for each tenant. With Kamaji, you can assign dedicated control planes to different teams, departments, or customers, giving them full control over their environments while sharing the underlying infrastructure.
- Capsule: Capsule is another project by Clastix that focuses on providing a multi-tenant environment in Kubernetes. It offers unique features that go beyond the standard Kubernetes primitives. With Capsule, you can create "Tenants" and assign them specific namespaces. Each tenant can have its own set of users, roles, and permissions.
Capsule also introduces the "Tenant Resources" concept, which allows you to define custom resource types specific to each tenant. - vCluster: developed by Loft Labs, takes a different approach to multi-tenancy by providing fully isolated virtual clusters. Each virtual cluster runs its own control plane and virtual nodes, giving you a dedicated Kubernetes cluster. With vCluster, you can create multiple virtual clusters within a single physical cluster, each with its own set of API servers, ETCD, and other control plane components.
Summary
In this blog post, we explored the concept of multi-tenancy and how Kubernetes is inherently designed to support multi-tenant environments. The very architecture of Kubernetes, with its focus on abstracting away the underlying infrastructure and providing a declarative approach to managing workloads, makes it a compelling choice for running multiple tenants on a shared cluster.
Additionally, we highlighted open-source tools like Kamaji, Capsule, and vCluster, which simplify the process of setting up and managing multi-tenancy in Kubernetes. These tools build upon Kubernetes' primitives and offer additional abstractions and management capabilities, making it even easier to implement and manage multi-tenancy in your clusters.
If you want to learn more about this topic, check out some of these additional resources from Civo: