Kubernetes Object Management

The kubectl command-line tool supports several different ways to create and manage Kubernetes objects. This document provides an overview of the different approaches. Read the Kubectl book for details of managing objects by Kubectl.

Management techniques

Imperative commands

When using imperative commands, a user operates directly on live objects in a cluster. The user provides operations to the kubectl command as arguments or flags.

This is the recommended way to get started or to run a one-off task in a cluster. Because this technique operates directly on live objects, it provides no history of previous configurations.

Examples

Run an instance of the nginx container by creating a Deployment object:

kubectl create deployment nginx --image nginx

Trade-offs

Advantages compared to object configuration:

• Commands are expressed as a single action word.
• Commands require only a single step to make changes to the cluster.

Disadvantages compared to object configuration:

• Commands do not integrate with change review processes.
• Commands do not provide an audit trail associated with changes.
• Commands do not provide a source of records except for what is live.
• Commands do not provide a template for creating new objects.

Imperative object configuration

In imperative object configuration, the kubectl command specifies the operation (create, replace, etc.), optional flags and at least one file name. The file specified must contain a full definition of the object in YAML or JSON format.

See the API reference for more details on object definitions.

Examples

Create the objects defined in a configuration file:

kubectl create -f nginx.yaml

Delete the objects defined in two configuration files:

kubectl delete -f nginx.yaml -f redis.yaml

Update the objects defined in a configuration file by overwriting the live configuration:

kubectl replace -f nginx.yaml

Trade-offs

Advantages compared to imperative commands:

• Object configuration can be stored in a source control system such as Git.
• Object configuration can integrate with processes such as reviewing changes before push and audit trails.
• Object configuration provides a template for creating new objects.

Disadvantages compared to imperative commands:

• Object configuration requires basic understanding of the object schema.
• Object configuration requires the additional step of writing a YAML file.

Advantages compared to declarative object configuration:

• Imperative object configuration behavior is simpler and easier to understand.
• As of Kubernetes version 1.5, imperative object configuration is more mature.

Disadvantages compared to declarative object configuration:

• Imperative object configuration works best on files, not directories.
• Updates to live objects must be reflected in configuration files, or they will be lost during the next replacement.

Declarative object configuration

When using declarative object configuration, a user operates on object configuration files stored locally, however the user does not define the operations to be taken on the files. Create, update, and delete operations are automatically detected per-object by kubectl. This enables working on directories, where different operations might be needed for different objects.

Examples

Process all object configuration files in the configs directory, and create or patch the live objects. You can first diff to see what changes are going to be made, and then apply:

kubectl diff -f configs/
kubectl apply -f configs/

Recursively process directories:

kubectl diff -R -f configs/
kubectl apply -R -f configs/

Trade-offs

Advantages compared to imperative object configuration:

• Changes made directly to live objects are retained, even if they are not merged back into the configuration files.
• Declarative object configuration has better support for operating on directories and automatically detecting operation types (create, patch, delete) per-object.

Disadvantages compared to imperative object configuration:

• Declarative object configuration is harder to debug and understand results when they are unexpected.
• Partial updates using diffs create complex merge and patch operations.

What's next

• Managing Kubernetes Objects Using Imperative Commands
• Imperative Management of Kubernetes Objects Using Configuration Files
• Declarative Management of Kubernetes Objects Using Configuration Files
• Declarative Management of Kubernetes Objects Using Kustomize
• Kubectl Command Reference
• Kubectl Book
• Kubernetes API Reference