kubectl apply vs create in Kubernetes - Performance Comparison

Time Complexity: kubectl apply vs create

O(n)

Understanding Time Complexity

We want to understand how the time to run kubectl apply and kubectl create changes as the number of Kubernetes resources grows.

How does the command's work grow when we manage more resources?

Scenario Under Consideration

Analyze the time complexity of these commands managing multiple resources.

kubectl create -f resources.yaml
kubectl apply -f resources.yaml

kubectl create makes new resources, while kubectl apply creates or updates resources by checking their current state.

Identify Repeating Operations

Look at what repeats when these commands run on many resources.

• Primary operation: For each resource, kubectl create sends a creation request once; kubectl apply first fetches the current state, then sends create or update requests.
• How many times: Once per resource for both commands, but apply does extra checks per resource.

How Execution Grows With Input

As the number of resources grows, the work grows roughly in a straight line.

Input Size (n)	Approx. Operations for create	Approx. Operations for apply
10	10 create requests	10 fetch + 10 create/update requests
100	100 create requests	100 fetch + 100 create/update requests
1000	1000 create requests	1000 fetch + 1000 create/update requests

Pattern observation: Both commands scale linearly, but apply does about twice the work per resource.

Final Time Complexity

Time Complexity: O(n)

This means the time grows directly with the number of resources you manage.

Common Mistake

[X] Wrong: "kubectl apply is always faster than kubectl create because it updates only changed resources."

[OK] Correct: apply always checks the current state first, so it does extra work per resource, making it slower when many resources are involved.

Interview Connect

Understanding how commands scale with resource count helps you design efficient deployment processes and shows you think about real-world system behavior.

Self-Check

What if we changed kubectl apply to use server-side apply? How would the time complexity change?

Practice

1. What is the main difference between kubectl create and kubectl apply?

easy

A. kubectl create only creates new resources and fails if they exist; kubectl apply creates or updates resources.

B. kubectl create updates existing resources; kubectl apply deletes resources.

C. kubectl create deletes resources; kubectl apply only creates new resources.

D. kubectl create and kubectl apply do the same thing.

Solution

1. Step 1: Understand kubectl create behavior

   kubectl create makes new resources but will fail if the resource already exists.

2. Step 2: Understand kubectl apply behavior

   kubectl apply can create new resources or update existing ones safely without failing.

3. Final Answer:

   kubectl create only creates new resources and fails if they exist; kubectl apply creates or updates resources. -> Option A

4. Quick Check:

   create = new only, apply = create or update [OK]

Hint: Create fails if exists; apply updates or creates [OK]

Common Mistakes:

• Thinking create updates existing resources
• Believing apply deletes resources
• Assuming both commands behave identically

2. Which of the following is the correct syntax to create a deployment using kubectl create?

easy

A. kubectl create deployment myapp --image=nginx

B. kubectl create pod myapp --image=nginx

C. kubectl apply deployment myapp --image=nginx

D. kubectl apply -f deployment.yaml

Solution

1. Step 1: Identify kubectl create syntax for deployment

   The command kubectl create deployment myapp --image=nginx creates a deployment named myapp with the nginx image.

2. Step 2: Differentiate from kubectl apply syntax

   kubectl apply uses the -f flag with a file, not direct deployment creation.

3. Final Answer:

   kubectl create deployment myapp --image=nginx -> Option A

4. Quick Check:

   create deployment uses direct command, apply uses files [OK]

Hint: Use 'create deployment' with image flag, apply uses files [OK]

Common Mistakes:

• Using apply syntax with create command
• Mixing file flag with create deployment
• Confusing create and apply commands

3. Given the commands below, what will happen if the deployment myapp already exists?

kubectl create deployment myapp --image=nginx
kubectl apply -f deployment.yaml

medium

A. Both commands will fail because the deployment exists.

B. Both commands will update the deployment.

C. The create command will update; the apply command will fail.

D. The create command will fail; the apply command will update the deployment.

Solution

1. Step 1: Behavior of kubectl create on existing resource

   kubectl create fails if the resource already exists, so the first command will fail.

2. Step 2: Behavior of kubectl apply on existing resource

   kubectl apply updates the existing resource safely, so the second command updates the deployment.

3. Final Answer:

   The create command will fail; the apply command will update the deployment. -> Option D

4. Quick Check:

   create fails if exists; apply updates [OK]

Hint: Create fails if exists; apply updates existing resources [OK]

Common Mistakes:

• Assuming create updates existing resources
• Thinking apply fails if resource exists
• Believing both commands behave the same

4. You ran kubectl create -f service.yaml but got an error saying the service already exists. What should you do to update the service instead?

medium

A. Use kubectl replace -f service.yaml to update the service.

B. Delete the service first, then run kubectl create -f service.yaml again.

C. Use kubectl apply -f service.yaml to update the existing service.

D. Run kubectl create -f service.yaml with a different name.

Solution

1. Step 1: Understand the error cause

   kubectl create fails if the resource exists, so the error means the service is already present.

2. Step 2: Choose the correct update method

   kubectl apply safely updates existing resources without deleting them, so use kubectl apply -f service.yaml.

3. Final Answer:

   Use kubectl apply -f service.yaml to update the existing service. -> Option C

4. Quick Check:

   apply updates existing resources safely [OK]

Hint: Use apply to update existing resources, not create [OK]

Common Mistakes:

• Trying to create again without deleting
• Deleting resources unnecessarily
• Using replace without understanding its effect

5. You want to manage a deployment over time, updating its image and replicas safely without deleting it. Which command should you use and why?

hard

A. Use kubectl create deployment myapp --image=nginx repeatedly to update the deployment.

B. Use kubectl apply -f deployment.yaml because it creates or updates resources safely.

C. Use kubectl delete deployment myapp then kubectl create -f deployment.yaml to update.

D. Use kubectl replace -f deployment.yaml because it creates new resources.

Solution

1. Step 1: Identify the need for safe updates over time

   Managing a deployment means updating it multiple times without deleting or failing.

2. Step 2: Choose the command that supports create or update safely

   kubectl apply can create or update resources safely, preserving existing settings and avoiding errors.

3. Step 3: Evaluate other options

   kubectl create fails if resource exists; deleting is disruptive; replace overwrites but is less safe than apply.

4. Final Answer:

   Use kubectl apply -f deployment.yaml because it creates or updates resources safely. -> Option B

5. Quick Check:

   Manage resources over time with apply [OK]

Hint: Apply manages updates safely; create is one-time only [OK]

Common Mistakes:

• Using create repeatedly causing errors
• Deleting resources unnecessarily
• Confusing replace with apply