A deployment describes the desired state of an application. It describes the number of replicas, but also the update strategy. Kubernetes will track the health of the pods and will remove or add pods when needed to comply with the desired state that is described in the deployment.

These deployments are specified in a YAML file. For example, when running a container in Kubernetes, you must specify a replica set. A replica set ensures that a specified number of pod replicas are running at any given time.