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kubectl Usage Conventions

Recommended usage conventions for kubectl.

• Using kubectl in Reusable Scripts
• Best Practices

Using kubectl in Reusable Scripts

For a stable output in a script:

• Request one of the machine-oriented output forms, such as -o name, -o json, -o yaml, -o go-template, or -o jsonpath.
• Fully-qualify the version. For example, jobs.v1.batch/myjob. This will ensure that kubectl does not use its default version that can change over time.
• Specify the --generator flag to pin to a specific behavior when you use generator-based commands such as kubectl run or kubectl expose.
• Don’t rely on context, preferences, or other implicit states.

Best Practices

kubectl run

For kubectl run to satisfy infrastructure as code:

• Tag the image with a version-specific tag and don’t move that tag to a new version. For example, use :v1234, v1.2.3, r03062016-1-4, rather than :latest (For more information, see Best Practices for Configuration).
• Capture the parameters in a checked-in script, or at least use --record to annotate the created objects with the command line for an image that is lightly parameterized.
• Check in the script for an image that is heavily parameterized.
• Switch to configuration files checked into source control for features that are needed, but not expressible via kubectl run flags.
• Pin to a specific generator version, such as kubectl run --generator=deployment/v1beta1.

Generators

You can create the following resources using kubectl run with the --generator flag:

If you do not specify a generator flag, other flags prompt you to use a specific generator. The following table lists the flags that force you to use specific generators, depending on the version of the cluster:

Note: These flags use a default generator only when you have not specified any flag. This means that when you combine --generator with other flags the generator that you specified later does not change. For example, in a cluster v1.4, if you initially specify --restart=Always, a Deployment is created; if you later specify --restart=Always and --generator=run/v1, a Replication Controller is created. This enables you to pin to a specific behavior with the generator, even when the default generator is changed later.

The flags set the generator in the following order: first the --schedule flag, then the --restart policy flag, and finally the --generator flag.

To check the final resource that was created, use the --dry-run flag, which provides the object to be submitted to the cluster.

kubectl apply

• You can use kubectl apply to create or update resources. However, to update a resource you should have created the resource by using kubectl apply or kubectl create --save-config. For more information about using kubectl apply to update resources, see Managing Resources.

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