The command-line interface allows users to run commands against Kubernetes clusters in the Kubernetes ecosystem. Two of the most commonly used commands are kubectl apply and kubectl create. Both commands are instrumental in managing Kubernetes resources, but they serve different purposes and come with their own set of functionalities. This article dives deep into the differences between kubectl apply and kubectl create, helping developers and system administrators decide when to use each command.
kubectl create
The kubectl create command is used to create a resource in a Kubernetes cluster. It can create one or multiple resources based on a file, standard input, or specifying command-line arguments. The create command is explicit and straightforward—it takes the definition of a resource, such as a pod, service, or deployment, and creates it in the cluster.
Key Characteristics of kubectl create:
- Immediacy: It creates resources immediately; if the resource already exists, it returns an error.
- Simplicity: Best suited for creating resources for the first time without needing updates or modifications.
- Non-idempotent: Running the same
kubectl createcommand multiple times will result in errors if the resource already exists, making it non-idempotent.
Example Usage of kubectl create:
To create resources defined in a YAML file:
kubectl create -f my-resource.yamlTo create a new namespace:
kubectl create namespace my-namespacekubectl apply
The kubectl apply command is used to apply a configuration change to a resource in a Kubernetes cluster. It takes a resource definition (usually from a YAML or JSON file) and applies the configuration to the resource. If the resource does not exist, kubectl apply will create it. If it does exist, kubectl apply will update it with the changes specified in the configuration file.
Key Characteristics of kubectl apply:
- Idempotency: The
applycommand is idempotent, meaning you can run it multiple times with the same configuration, and Kubernetes will ensure the resource matches the desired state described by the configuration. - Declarative Configuration: It embraces a declarative approach to resource management, where you declare the desired state of the resource. Kubernetes works to make the actual state match the desired state.
- Update and Create: It can create new resources and update existing ones with new configurations.
Example Usage of kubectl apply:
To apply configurations from a YAML file:
kubectl apply -f my-resource.yamlTo apply configurations to all resources defined in a directory:
kubectl apply -f /path/to/my-resources/When to Use kubectl create vs. kubectl apply
Choosing between kubectl create and kubectl apply depends on the specific needs of your deployment process and resource management strategy.
- Use
kubectl createwhen:- You need to create resources explicitly and ensure they do not already exist.
- You are working with resources that won’t need immediate updates or modifications.
- You prefer a command that fails when a resource already exists, as a safeguard against unintended duplication.
- Use
kubectl applywhen:- You are managing resources declaratively, especially as part of a CI/CD pipeline.
- You want a single command that can handle creation and resource updates.
- You prefer to maintain a configuration file as the source of truth for your resources.
Conclusion
Both kubectl create and kubectl apply are fundamental commands in Kubernetes for managing resources. kubectl create is ideal for straightforward, one-off resource creation, offering simplicity and immediacy. On the other hand, kubectl apply supports a more complex, declarative approach to resource management, suitable for updating resources and maintaining idempotency. Understanding each command’s nuances and appropriate use cases is key to effectively managing resources in Kubernetes environments.
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