130 lines
4.2 KiB
Markdown
130 lines
4.2 KiB
Markdown
---
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title: Imperative Management of Kubernetes Objects Using Configuration Files
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---
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{% capture overview %}
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Kubernetes objects can be created, updated, and deleted by using the `kubectl`
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command-line tool along with an object configuration file written in YAML or JSON.
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This document explains how to define and manage objects using configuration files.
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{% endcapture %}
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{% capture body %}
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## Trade-offs
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The `kubectl` tool supports three kinds of object management:
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* Imperative commands
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* Imperative object configuration
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* Declarative object configuration
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See [Kubernetes Object Management](/docs/concepts/tools/kubectl/object-management-overview/)
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for a discussion of the advantages and disadvantage of each kind of object management.
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## How to create objects
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You can use `kubectl create -f` to create an object from a configuration file.
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Refer to the [kubernetes object schema reference](/docs/resources-reference/v1.5/)
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for details.
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- `create -f <filename|url>`
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## How to update objects
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You can use `kubectl replace -f` to update a live object according to a
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configuration file.
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- `replace -f <filename|url>`
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## How to delete objects
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You can use `kubectl delete -f` to delete an object that is described in a
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configuration file.
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- `delete -f <filename|url>`
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## How to view an object
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You can use `kubectl get -f` to view information about an object that is
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described in a configuration file.
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- `get -f <filename|url> -o yaml`
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The `-o yaml` flag specifies that the full object configuration is printed.
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Use `get -h` to see a list of options.
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## Limitations
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The `create`, `replace`, and `delete` commands work well when each object's
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configuration is fully defined and recorded in its configuration
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file. However when a live object is updated, and the updates are not merged
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into its configuration file, the updates will be lost the next time a `replace`
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is executed. This is can happen if a controller, such as
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a HorizontalPodAutoscaler, makes updates directly to a live object. Here's
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an example:
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1. You create an object from a configuration file.
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1. Another source updates the object by changing some field.
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1. You replace the object from the configuration file. Changes made by
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the other source in step 2 are lost.
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If you need to support multiple writers to the same object, you can use
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`kubectl apply` to manage the object.
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## Creating and editing an object from a URL without saving the configuration
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Suppose you have the URL of an object configuration file. You can use
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`kubectl create --edit` to make changes to the configuration before the
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object is created. This is particularly useful for tutorials and tasks
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that point to a configuration file that could be modified by the reader.
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```sh
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kubectl create -f <url> --edit
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```
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## Migrating from imperative commands to imperative object configuration
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Migrating from imperative commands to imperative object configuration involves
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several manual steps.
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1. Export the live object to a local object configuration file:
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kubectl get <kind>/<name> -o yaml --export > <kind>_<name>.yaml
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1. Manually remove the status field from the object configuration file.
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1. For subsequent object management, use `replace` exclusively.
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kubectl replace -f <kind>_<name>.yaml
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## Defining controller selectors and PodTemplate labels
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**Warning**: Updating selectors on controllers is strongly discouraged.
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The recommended approach is to define a single, immutable PodTemplate label
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used only by the controller selector with no other semantic meaning.
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Example label:
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```yaml
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selector:
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matchLabels:
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controller-selector: "extensions/v1beta1/deployment/nginx"
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template:
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metadata:
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labels:
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controller-selector: "extensions/v1beta1/deployment/nginx"
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```
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{% endcapture %}
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{% capture whatsnext %}
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- [Managing Kubernetes Objects Using Imperative Commands](/docs/concepts/tools/kubectl/object-management-using-imperative-commands/)
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- [Managing Kubernetes Objects Using Object Configuration (Declarative)](/docs/concepts/tools/kubectl/object-management-using-declarative-config/)
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- [Kubectl Command Reference](/docs/user-guide/kubectl/v1.5/)
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- [Kubernetes Object Schema Reference](/docs/resources-reference/v1.5/)
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{% endcapture %}
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{% include templates/concept.md %}
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