Mastering Kubernetes: Understanding the Nuances of kubectl create vs kubectl apply

Mastering Kubernetes: Understanding the Nuances of kubectl create vs kubectl apply

The kubectl create and kubectl apply commands are fundamental tools in Kubernetes for managing resources, but they serve slightly different purposes and are used in different scenarios. Understanding the distinction between these commands is crucial for effective Kubernetes administration.

kubectl create

kubectl create is used to create a new resource in Kubernetes. It can be used to create one or more resources from a file or from stdin.

• Use Cases: Ideal for creating new resources where the primary concern is the initial creation.
• Behavior: It creates a new resource and fails if the resource already exists.
• Example Command:

kubectl create -f pod.yaml

• Implications:
• Not idempotent: Running kubectl create on the same file multiple times results in errors if the resource already exists.
• Primarily used for one-off creations rather than management of resources.

kubectl apply

kubectl apply is used to apply a configuration change to a resource. It can be used to create or update resources in a declarative manner.

• Use Cases: Ideal for configuration management where resources may need to be updated repeatedly.
• Behavior:
  • If the resource does not exist, kubectl apply will create it.
  • If the resource exists, kubectl apply updates the resource with the changes specified in the configuration file. It achieves this by comparing the configuration file with the current state and applying the changes.
• Example Command:

kubectl apply -f pod.yaml

• Implications:
  • Idempotent: You can run kubectl apply multiple times on the same resource without causing errors. This makes it suitable for automated environments and CI/CD pipelines.
  • Uses and updates the last-applied-configuration annotation of resources, which helps Kubernetes know how to update resources and handle changes.

Key Differences

1. Idempotence:

   • create: Not idempotent. Re-running the command on the same resource definition without changes will result in an error if the resource already exists.
   • apply: Idempotent. It can be run repeatedly on the same resource definition without adverse effects, making it suitable for updates.

2. Update Mechanism:

   • create: Cannot update a resource. It is purely for creation.
   • apply: Can create or modify a resource based on the resource’s existence and the changes defined in the YAML file.

3. Annotation Usage:

   • create: Does not manage the kubectl.kubernetes.io/last-applied-configuration annotation.
   • apply: Stores the current configuration in the last-applied-configuration annotation to track resource changes over time.

Choosing Between create and apply

• Use kubectl create when you need a simple and direct way to create new resources and are sure they do not exist.
• Use kubectl apply for more complex deployments where updates over time are expected. This is particularly useful in development workflows, CI/CD pipelines, and in situations where you might need to tweak configurations iteratively.

Understanding these commands and their implications helps in choosing the right tool for managing resources effectively in Kubernetes environments.