Whether you need a single Kubernetes cluster or multiple clusters to containerize your applications in a manageable way can be daunting. A single cluster might be suitable at the inception of your application, but as the operation grows, so does the risk potential.
Multiple clusters may be more appropriate for the portability of your workload. Users who opt for multiple clusters will benefit from using a Kubernetes management platform.
A Kubernetes cluster is a set of nodes that run containerized applications. Typically, containerizing applications package an app with its dependencies and some necessary services. The flexibility of Kubernetes clusters permits applications to be developed more easily, moved, and arranged by software creators than other virtual machines.
You can operate a given set of workloads on either a few large clusters (containing multiple workloads per cluster) or many clusters (containing few workloads per cluster) or blend these two modes.
Each approach has pros and cons, and understanding the tradeoffs will ultimately inform your decision on which to take to best manage your applications. In addition, you can decide for yourself how many Kubernetes clusters you need.
The software developer’s dilemma
Software creators seldom manage a single application at a time but divvy their attention among multiple they are either in the process of perfecting or already operating. Additionally, there may be numerous instances of a single application across various environments, depending on its developmental stage.
Each application instance is its own self-contained deployment unit that can function independently. For the Kubernetes user, this raises specific questions about whether or not a single large cluster or multiple small clusters is more efficient.
The good news is, whichever you choose, it is valid within the Kubernetes system that is adaptable to its users’ preferences.
Kubernetes reminds users that Kubernetes supports clusters up to 5000 nodes at v1.12 and supports configurations that meet all of the following criteria:
- No more than 5000 nodes
- No more than 150,000 total pods
- No more than 300,000 total containers
- No more than 100 pods per node
Bearing this in mind, software creators can then evaluate their options by examining two approaches on either end of the spectrum: one large shared cluster versus many small clusters, as well as delve into the benefits and drawbacks of each organizational method.
A single large shared cluster
This approach can be considered a general infrastructure platform, with all of your apps compiled into a single location where you can launch whatever you need to the existing Kubernetes cluster.
Kubernetes allows users to create separate namespaces for individual applications within a said cluster, enabling you to differentiate between them and avoid confusion. Think of this mechanism as analogous to folders on your smartphone!
- Efficient use of resources as you only need one copy per cluster.
- One Kubernetes cluster is cheaper than running multiple, as you are billed per node.
- Administration is more efficient as maintenance boils down to a single cluster and authorization set-up is less complicated.
- If one application breaks, the entire cluster can shut down.
- No hard security isolation because unrelated apps interact with one another.
- Many users mean multiple people are accessing the cluster at a given time.
- Limited space within a cluster, which only supports so many nodes.
Many small clusters
In this organizational scenario, you have a Kubernetes cluster for every single application instance, meaning every deployment unit has its own compartment that the user manages independently of its counterparts. If the “single large cluster” method is considered “general infrastructure,” then comparably, this approach is more akin to giving every application instance its own special runtime.
- If one cluster breaks, it does not damage the others because they are unrelated.
- Workloads in one cluster do not share resources with other clusters.
- More secure because unrelated applications do not interact and share data.
- Fewer individuals have access to the system for a given application.
- Inefficient resource usage as each cluster requires its own management system.
- Comparatively more expensive (although Kubernetes management platforms can negate some of this expense by offering services at a fixed rate).
- Administration for each cluster is more complex because one must set up authorization and management individually for each Kubernetes cluster.
Deciding how many Kubernetes clusters you need can be determined based on several factors: the number of applications you are operating, your budget, your security preferences, your experience administrating complex systems, and more.
You may conclude that a hybridized system works best for you, and that is okay. Kubernetes offers its users the maneuverability to choose the type of organizational system that meets their specifications without forcing them to break their bank overseeing multiple clusters. There are platforms geared toward cluster management that offer excellent service at an affordable rate, so you do not have to fear handling numerous Kubernetes clusters on your own.