Kubernetes objects can be created, updated, and deleted by using the kubectl
command-line tool along with an object configuration file written in YAML or JSON.
This document explains how to define and manage objects using configuration files.
The kubectl
tool supports three kinds of object management:
See Kubernetes Object Management for a discussion of the advantages and disadvantage of each kind of object management.
You can use kubectl create -f
to create an object from a configuration file.
Refer to the kubernetes API reference
for details.
kubectl create -f <filename|url>
Warning: Updating objects with thereplace
command drops all parts of the spec not specified in the configuration file. This should not be used with objects whose specs are partially managed by the cluster, such as Services of typeLoadBalancer
, where theexternalIPs
field is managed independently from the configuration file. Independently managed fields must be copied to the configuration file to preventreplace
from dropping them.
You can use kubectl replace -f
to update a live object according to a
configuration file.
kubectl replace -f <filename|url>
You can use kubectl delete -f
to delete an object that is described in a
configuration file.
kubectl delete -f <filename|url>
You can use kubectl get -f
to view information about an object that is
described in a configuration file.
kubectl get -f <filename|url> -o yaml
The -o yaml
flag specifies that the full object configuration is printed.
Use kubectl get -h
to see a list of options.
The create
, replace
, and delete
commands work well when each object’s
configuration is fully defined and recorded in its configuration
file. However when a live object is updated, and the updates are not merged
into its configuration file, the updates will be lost the next time a replace
is executed. This can happen if a controller, such as
a HorizontalPodAutoscaler, makes updates directly to a live object. Here’s
an example:
If you need to support multiple writers to the same object, you can use
kubectl apply
to manage the object.
Suppose you have the URL of an object configuration file. You can use
kubectl create --edit
to make changes to the configuration before the
object is created. This is particularly useful for tutorials and tasks
that point to a configuration file that could be modified by the reader.
kubectl create -f <url> --edit
Migrating from imperative commands to imperative object configuration involves several manual steps.
Export the live object to a local object configuration file:
kubectl get <kind>/<name> -o yaml --export > <kind>_<name>.yaml
Manually remove the status field from the object configuration file.
For subsequent object management, use replace
exclusively.
kubectl replace -f <kind>_<name>.yaml
Warning: Updating selectors on controllers is strongly discouraged.
The recommended approach is to define a single, immutable PodTemplate label used only by the controller selector with no other semantic meaning.
Example label:
selector:
matchLabels:
controller-selector: "extensions/v1beta1/deployment/nginx"
template:
metadata:
labels:
controller-selector: "extensions/v1beta1/deployment/nginx"
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