Kubernetes Deployments Explained: What They Are and Why They MatterKubernetes Deployments Explained: What They Are and Why They MatterKubernetes Deployments Explained: What They Are and Why They Matter
A Kubernetes deployment is more than just running an application — it's a streamlined way to manage stateless workloads, automate scaling, and simplify infrastructure management.
If you're new to Kubernetes, you might assume that the meaning of Kubernetes deployment is self-evident and refers to the deployment of any type of workload within a Kubernetes cluster.
In fact, though, deployment has a more specific definition within Kubernetes , the open source container orchestrator — and understanding precisely what a deployment is in this context is a step toward understanding how to use Kubernetes itself to maximum effect.
So, let's break down exactly what a Kubernetes deployment is, what makes it different from other ways of deploying workloads using Kubernetes, and why the very concept of a deployment is so central to how Kubernetes works.
Kubernetes Deployment: The Simple Definition
To begin with, let's clarify that, in a simple sense, a Kubernetes deployment does indeed refer to an application that someone has deployed on Kubernetes.
More specifically, a deployment is one or more pods (a pod is one or more containers ) that comprise an application. Kubernetes admins configure deployments by writing code describing which pods and containers the deployment should include, along with other optional parameters.
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For instance, here's YAML code that describes a deployment for NGINX , the open source web server application:
apiVersion: apps/v1
kind: Deployment
metadata:
name: nginx-deployment
selector:
matchLabels:
app: nginx
template:
metadata:
labels:
app: nginx
spec:
containers:
- name: nginx
image: nginx:latest
ports:
- containerPort: 80So, if you think of a deployment as a way of running an application in Kubernetes, you're not wrong — but there's more to it than that.
The Precise Meaning of Kubernetes Deployment
That's because a deployment isn't the only way to run an app on Kubernetes. There are several other methods, which we'll discuss in a moment.
For now, let's cover what makes a deployment distinct from other ways of running workloads on Kubernetes:
Deployments are usually used to run stateless applications, meaning ones that don't need to store data persistently.
In a deployment, pods are treated as interchangeable; there is no simple way of assigning pods unique identities or controlling the order in which they start when you use a deployment to run an application.
Typically, deployments don't tell Kubernetes how many copies of a pod to run or which node should host the pods, although it's possible to define these options by adding parameters to the deployment configuration.
These characteristics distinguish deployments from the two other main ways of running applications in Kubernetes, which are:
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StatefulSets, which include unique pod identities and enable persistent storage. Unlike deployments, StatefulSets are usually used when running an application that is stateful , meaning it needs to retain data persistently between shutdown and restart events.
ReplicaSets, which tell Kubernetes to run a particular number of copies of a pod at all times. ReplicaSets are often configured within deployments using the replicas: parameter, but a ReplicaSet is distinct from the deployment of which it's a part.
What to Use When: Deployments vs. StatefulSets vs. ReplicaSets
In general, if you want to run a simple application on Kubernetes, it makes sense to deploy it as a deployment. This is simplest and fastest.
But if the app has special requirements, like the need for persistent storage or multiple replicas, you'd want to choose a StatefulSet or ReplicaSet instead.
Why It All Matters
Understanding the full context of the meaning of Kubernetes deployments is important beyond the task of choosing the right application hosting approach.
It also matters because when you appreciate the concept at the core of deployments (and, for that matter, StatefulSets and ReplicaSets), you're in a better position to appreciate the concepts at the core of Kubernetes.
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Those concepts are, above all, the notion that admins shouldn't have to make unnecessary configuration decisions when deploying applications. The beauty of a deployment is that it lets you tell Kubernetes which pod you want to run, and Kubernetes then does the work necessary to decide which server within your cluster should host the pod, start the pod, monitor the pod as it runs, and restart it if it crashes.
In a traditional approach to application deployment, you'd have to do these things manually. You'd have to choose which server to host the app, manually start it, restart it if it stops, and so on.Kubernetes does let you configure additional parameters for applications that require them — which is why you may sometimes prefer a StatefulSet or ReplicaSet over a deployment. But with a simple deployment, you configure the bare minimum code necessary to govern how an app runs and then sit back while Kubernetes runs it. That's a large part of what makes Kubernetes so powerful.
About the Author
Technology analyst, Fixate.IO
Christopher Tozzi is a technology analyst with subject matter expertise in cloud computing, application development, open source software, virtualization, containers and more. He also lectures at a major university in the Albany, New York, area. His book, "For Fun and Profit: A History of the Free and Open Source Software Revolution ," was published by MIT Press.
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