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- Apply Creates and Updates Resources in a cluster through running
kubectl applyon Resource Config.
- Apply manages complexity such as ordering of operations and merging user defined and cluster defined state.
Apply is a command that will update a Kubernetes cluster to match state defined locally in files.
- Fully declarative - don't need to specify create or update - just manage files
- Merges user owned state (e.g. Service
selector) with state owned by the cluster (e.g. Service
- Resources: Objects in a cluster - e.g. Deployments, Services, etc.
- Resource Config: Files declaring the desired state for Resources - e.g. deployment.yaml. Resources are created and updated using Apply with these files.
kubectl apply Creates and Updates Resources through local or remote files. This may be through either raw Resource Config or kustomization.yaml.
Though Apply can be run directly against Resource Config files or directories using
-f, it is recommended
to run Apply against a
kustomization.yaml allows users to define
configuration that cuts across many Resources (e.g. namespace).
# kustomization.yaml apiVersion: kustomize.config.k8s.io/v1beta1 kind: Kustomization # list of Resource Config to be Applied resources: - deployment.yaml # namespace to deploy all Resources to namespace: default # labels added to all Resources commonLabels: app: example env: test
# deployment.yaml apiVersion: apps/v1 kind: Deployment metadata: name: nginx labels: component: nginx tier: frontend spec: selector: matchLabels: component: nginx tier: frontend template: metadata: labels: component: nginx tier: frontend spec: containers: - name: nginx image: nginx:1.15.4
Users run Apply on directories containing
kustomization.yaml files using
-k or on raw
ResourceConfig files using
# Apply the Resource Config kubectl apply -k . # View the Resources kubectl get -k .
A single Resource Config file may declare multiple Resources separated by
Any Resources that do not exist and are declared in Resource Config when Apply is run will be Created.
Any Resources that already exist and are declared in Resource Config when Apply is run may be Updated.
Any fields that have been added to the Resource Config will be set on the Resource.
Any fields that contain different values for the fields specified locally in the Resource Config from what is in the Resource will be updated by merging the Resource Config into the live Resource. See merging for more details.
Fields that were in the Resource Config the last time Apply was run, will be deleted from the Resource, and return to their default values.
Fields that were not specified in the Resource Config but are set on the Resource will be left unmodified.
Declarative deletion of Resources does not yet exist in a usable form, but is under development.
In some cases, it may be useful to automatically Apply changes when ever the Resource Config is changed.
This example uses the unix
watch command to periodically invoke Apply against a target.
watch -n 60 kubectl apply -k https://github.com/myorg/myrepo
Resource Creation Ordering
Certain Resource Types may be dependent on other Resource Types being created first. e.g. Namespaced Resources on the Namespaces, RoleBindings on Roles, CustomResources on the CRDs, etc.
When used with a
kustomization.yaml, Apply sorts the Resources by Resource type to ensure Resources
with these dependencies are created in the correct order.