Objects In Kubernetes [page]deterministic

This page explains how Kubernetes objects are represented in the Kubernetes API, and how you can express them in `.yaml` format.

## Understanding Kubernetes objects {#kubernetes-objects}

*Kubernetes objects* are persistent entities in the Kubernetes system. Kubernetes uses these entities to represent the state of your cluster. Specifically, they can describe:

* What containerized applications are running (and on which nodes) * The resources available to those applications * The policies around how those applications behave, such as restart policies, upgrades, and fault-tolerance

A Kubernetes object is a "record of intent"--once you create the object, the Kubernetes system will constantly work to ensure that the object exists. By creating an object, you're effectively telling the Kubernetes system what you want your cluster's workload to look like; this is your cluster's *desired state*.

To work with Kubernetes objects—whether to create, modify, or delete them—you'll need to use the [Kubernetes API](/docs/concepts/overview/kubernetes-api/). When you use the `kubectl` command-line interface, for example, the CLI makes the necessary Kubernetes API calls for you. You can also use the Kubernetes API directly in your own programs using one of the [Client Libraries](/docs/reference/using-api/client-libraries/).

### Object spec and status

Almost every Kubernetes object includes two nested object fields that govern the object's configuration: the object *`spec`* and the object *`status`*. For objects that have a `spec`, you have to set this when you create the object, providing a description of the characteristics you want the resource to have: its _desired state_.

The `status` describes the _current state_ of the object, supplied and updated by the Kubernetes system and its components. The Kubernetes [control plane](#gloss:control-plane) continually and actively manages every object's actual state to match the desired state you supplied.

For example: in Kubernetes, a Deployment is an object that can represent an application running on your cluster. When you create the Deployment, you might set the Deployment `spec` to specify that you want three replicas of the application to be running. The Kubernetes system reads the Deployment spec and starts three instances of your desired application--updating the status to match your spec. If any of those instances should fail (a status change), the Kubernetes system responds to the difference between spec and status by making a correction--in this case, starting a replacement instance.

For more information on the object spec, status, and metadata, see the [Kubernetes API Conventions](https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md).

### Describing a Kubernetes object

When you create an object in Kubernetes, you must provide the object spec that describes its desired state, as well as some basic information about the object (such as a name). When you use the Kubernetes API to create the object (either directly or via `kubectl`), that API request must include that information as JSON in the request body. Most often, you provide the information to `kubectl` in a file known as a _manifest_. By convention, manifests are YAML (you could also use JSON format). Tools such as `kubectl` convert the information from a manifest into JSON or another supported serialization format when making the API request over HTTP.

Here's an example manifest that shows the required fields and object spec for a Kubernetes Deployment:

One way to create a Deployment using a manifest file like the one above is to use the [`kubectl apply`](/docs/reference/generated/kubectl/kubectl-commands#apply) command in the `kubectl` command-line interface, passing the `.yaml` file as an argument. Here's an example:

```shell kubectl apply -f https://k8s.io/examples/application/deployment.yaml ```

The output is similar to this:

``` deployment.apps/nginx-deployment created ```

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