Linux Tactic

Kubectl Apply vs Create: Choosing the Right Approach for Successful Kubernetes Management

Kubectl Apply vs Create: Understanding the Difference

If youre managing Kubernetes clusters, youre likely familiar with the two primary approaches to making changes: imperative and declarative. The kubectl command-line tool in Kubernetes offers two commands to perform these approaches – kubectl apply and kubectl create.

While both can accomplish the same task, they have distinct differences. Imperative Management: Kubectl Create

The kubectl create command takes an input file in the form of a YAML or JSON file and sends it to the Kubernetes API to create the necessary object(s).

It is an imperative approach, meaning that you tell Kubernetes exactly what to do by issuing command lines. Additionally, it behaves as if there is no existing object, creating a new one each time the file is executed.

This approach can be useful when you are creating an object for the first time, but it is not a good option when trying to make changes to existing objects. Declarative Management: Kubectl Apply

Kubectl apply operates in a very different way.

Unlike the kubectl create command, kubectl apply takes a live object as input rather than a YAML or JSON file. It will only enact the changes required to achieve your desired state, instead of recreating the object each time.

This command is declarative since you describe the desired state, and Kubernetes figures out the changes required to reach that state. To understand the difference between these two approaches, let’s take a look at some examples.

Example: Creating a Pod using Imperative Approach

To create a new Pod using kubectl create, you need to create a YAML file with the appropriate specifications such as pod name, image, etc. Then, you can execute the following command:

“`

kubectl create -f pod.yaml

“`

Here, Kubernetes will take the entire YAML file as input and create a new Pod taking the specs specified in it.

While this approach works, it becomes difficult to make changes to it later on. Example: Editing Pod YAML File and Using Imperative Approach to Apply Changes

Lets assume you need to make some changes to the Pod created above.

For instance, you now want to change its name to something else. You need to edit the YAML file and execute the following command:

“`

kubectl apply -f pod.yaml

“`

However, Kubernetes returns an error because you’re trying to apply a file that already exists.

To overcome this, you could instead use the kubectl replace command. But this approach does not make sense as it still tries to create the object from scratch rather than updating the existing object.

Example: Using Declarative Approach to Apply Changes

Instead of editing the YAML file, you could use a declarative approach to update the Pod. If the Pod’s existing YAML file is as follows:

“`

apiVersion: v1

kind: Pod

metadata:

name: test-pod

spec:

containers:

– name: nginx

image: nginx:1.7.9

ports:

– containerPort: 80

“`

To update the Pod’s container image to 1.8.0, you can create a new YAML file such as this:

“`

apiVersion: v1

kind: Pod

metadata:

name: test-pod

spec:

containers:

– name: nginx

image: nginx:1.8.0

ports:

– containerPort: 80

“`

Then, execute the below command:

“`

kubectl apply -f pod.yaml

“`

Here, Kubernetes compares the desired state with the live state and applies only the necessary changes.

The Pod’s name is not part of the updated YAML file, so it remains unchanged, but the container image is updated to 1.8.0.

Verifying Changes

Once you execute the kubectl apply command, it’s essential to verify that the changes you requested took effect. This is where kubectl diff comes in handy.

It lets you compare the live object with its associated configuration file or stdin.

“`

$ kubectl diff -f pod.yaml

“`

If the diff utility indicates that there are no changes between the live object and its desired state, it means that your previous kubectl apply command was successful.

Conclusion

kubectl create and kubectl apply commands let you manage your Kubernetes environment through a declarative and imperative approach, respectively. Its important to understand the difference between these two commands and when to use them.

You can use a declarative approach to update your Kubernetes objects, which would help you to reduce the risk of errors that arise from editing YAML files manually and forgetting to document the changes. Kubectl create or apply?

Which one to use? When managing a Kubernetes environment, it’s essential to understand the differences between kubectl create and kubectl apply.

Knowing how and when to use these two commands can make the process of managing Kubernetes more manageable and efficient. Here, we will cover the typical use cases for each command.

Use Cases for Kubectl Apply

Kubectl apply is a declarative approach that takes a live object as input and only makes changes required to achieve the desired state. This command is useful in the following scenarios:

1.

Version Control: Version control is critical when managing your Kubernetes objects. Kubectl apply reads a YAML or JSON file and applies it to a live Kubernetes object, ensuring that youre always using the latest and most up-to-date version.

This ensures that your Kubernetes objects are always in sync with your version control system. 2.

Accuracy of Data: When dealing with Kubernetes objects, it’s essential to keep track of changes made to them. Using kubectl apply overwrites only the properties of the object that have changed, meaning that you can accurately track the changes that took place.

This is especially important when you are making significant changes to Kubernetes objects, and you need to ensure the accuracy of your data. 3.

Managing K8s Objects: Kubernetes objects can be complex and have many different properties. Kubectl apply lets you manage these objects more efficiently without worrying about the technical details.

The command reads the desired state from your YAML or JSON files and compares it directly to the live Kubernetes object. It then applies any necessary changes, making it much easier to manage these objects.

Use Cases for Kubectl Create

Kubectl create is an imperative approach that takes an input file in the form of YAML or JSON and sends it directly to the Kubernetes API. It behaves as if there is no existing object, creating a new one every time it is executed.

It is useful in the following scenarios:

1. Troubleshooting: When trying to troubleshoot why a Kubernetes object isn’t working, you can use the kubectl create command to create a new object from scratch.

You can then compare the new object’s properties to the existing object to identify the issue. 2.

Learning: If you’re learning Kubernetes, using kubectl create is an excellent way to experiment with different objects and configuration options. You can create objects quickly and efficiently, experimenting with ways to use them in your application or infrastructure.

3. Interactive Experimentation: With kubectl create, you can experiment interactively, issuing an initial command and then tailoring additional parameters to fit your needs.

This approach can be useful when you need to create complex objects that require a particular configuration.

Conclusion

In conclusion, kubectl create and kubectl apply have different use cases, and it’s essential to know when to use each one. Kubectl create is useful for troubleshooting, learning, and interactive experimentation, while kubectl apply is reliable for managing Kubernetes objects, ensuring version control and the accuracy of your data.

By understanding the differences between these two commands, you can more efficiently manage your Kubernetes environment and make it more efficient and effective. In summary, the difference between “kubectl create” and “kubectl apply” is fundamental to Kubernetes management.

Both imperative and declarative approaches have their uses in different scenarios. Those who are new to Kubernetes should use “kubectl create” for troubleshooting, learning, and interactive experimentation; while “kubectl apply” is an ideal choice for managing Kubernetes objects, ensuring version control, and the accuracy of your data.

By understanding the differences between these two commands, you can manage your Kubernetes environment more efficiently and effectively. In conclusion, the proper usage of the “kubectl create” and “kubectl apply” commands is fundamental to managing Kubernetes efficiently and effectively.

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