In some ways, deciding whether to use multiple namespaces or multiple clusters to segment workloads in Kubernetes is what you might call a first-world problem: If you're making this choice, you're in the fortunate position of having the resources and flexibility necessary to build whichever Kubernetes architecture best suits your needs.
Still, deciding between multiple namespaces within one cluster or multiple clusters can be a tough choice. Here's a breakdown of the pros and cons of each approach.
Kubernetes Namespaces vs. Clusters
First, let's define the terms.
A Kubernetes namespace is a virtual resource that isolates one workload from another within the same Kubernetes cluster. By default, most applications that you deploy in one namespace can't see or communicate with those running in other namespaces — even though they are all running within the same cluster and are hosted by the same physical servers.
A Kubernetes cluster, meanwhile, is a distinct set of nodes. Any workloads running on those nodes are completely isolated from each other by default.
Multiple Kubernetes namespaces can run within a cluster, but you can't have multiple clusters associated with the same namespace. You can, however, manage multiple Kubernetes clusters via a single control plane — a practice that is becoming more and more common. This means you can manage all of your clusters using a single set of Kubernetes tools instead of having to install a different Kubernetes instance for each cluster.
Multiple Kubernetes Namespaces vs. Multiple Clusters
So, which approach is better if you have Kubernetes workloads that you want to isolate from each other — multiple namespaces on one cluster or multiple clusters managed via a single control plane?
The answer depends on your setup and priorities. Here's an overview of how to decide.
The Pros and Cons of Multiple Namespaces
The main advantage of using multiple namespaces is that it's simpler. You can easily create a new namespace with a single command, such as:
kubectl create namespace yournewnamespace
It's also easier to manage multiple namespaces. If you want to apply role-based access control (RBAC) policies across several Kubernetes namespaces, for instance, you can simply create a ClusterRole instead of a Role. In other words, most of Kubernetes' native tooling lets you work with multiple spaces by default, without any special configurations or extensions.
On the other hand, the major downside of using multiple namespaces is that it provides less isolation. This could translate to security or privacy issues in the event that a workload running in one namespace manages to interact with another namespace in a way it shouldn't. There are two main ways for this to happen:
- Configuration mistakes, such as ill-defined ClusterRoles, by which you accidentally allow workloads to interact across namespaces. This is the main risk that arises from multiple namespaces.
- Security bugs in Kubernetes that attackers can exploit in order to escalate a breach from one namespace into others. Realistically speaking, this is not likely to be an issue. But it's a possibility.
Either way, you get less guarantee of isolation between workloads when you use multiple namespaces.
The Pros and Cons of Multiple Clusters
The main reason to set up multiple clusters is that it does provide rigid isolation between workloads. Even if you manage each of your clusters through a single control plane, you'd have to go out of your way to create configurations that accidentally integrate workloads running in separate clusters.
Likewise, although it's possible for security vulnerabilities to enable breaches to spread between clusters, the potential risk here is lower, given that most tooling in Kubernetes is designed to interact with single clusters.
On the other hand, the fact that Kubernetes tooling is designed with single clusters in mind by default also means that multiple clusters are harder to set up and manage via one control plane. You can certainly do it, but you need to figure out ways to keep the control plane data in sync across all clusters. You also need to configure networking in such a way that the clusters can all communicate with the control plane — while also, ideally, preventing inter-cluster communication unless you require it.
These are both significant challenges, and Kubernetes' native tooling doesn't really address them. Projects such as Virtual Kubelet do, but using them requires adding more tools to your Kubernetes tool set.
The bottom line: If security and isolation are your top priority, and you have the expertise on hand to manage complex Kubernetes architectures, go with multiple clusters. But if you just want a simple, relatively secure way to isolate workloads, then create multiple namespaces within one cluster while taking steps to avoid configuration mistakes that could expose your namespaces to each other in unintended ways.