> ## Documentation Index
> Fetch the complete documentation index at: https://notes.kodekloud.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Solution Deploymentoptional
> This guide introduces Kubernetes deployments and explains how to verify the environment and troubleshoot deployment issues.
In this guide, we introduce Kubernetes deployments by first examining the current environment state before any deployment is created.
## Environment Verification
Start by checking how many pods exist on the system with the command:
```bash theme={null}
kubectl get pods
```
Output:
```plaintext theme={null}
No resources found in default namespace.
```
Next, verify the number of ReplicaSets:
```bash theme={null}
kubectl get rs
```
Output:
```plaintext theme={null}
No resources found in default namespace.
```
Finally, check the existing deployments:
```bash theme={null}
kubectl get deployments
```
Output:
```plaintext theme={null}
No resources found in default namespace.
```
At this point, the environment is clean—no pods, ReplicaSets, or deployments are present.
Some changes are then applied. Rechecking the deployments now shows that one deployment has been created:
```bash theme={null}
kubectl get deployments
```
Output:
```plaintext theme={null}
NAME READY UP-TO-DATE AVAILABLE AGE
frontend-deployment 0/4 4 0 10s
```
Next, inspect the ReplicaSets:
```bash theme={null}
kubectl get rs
```
Output:
```plaintext theme={null}
NAME DESIRED CURRENT READY AGE
frontend-deployment-7f8dcd896 4 4 0 35s
```
And finally, list the pods:
```bash theme={null}
kubectl get pods
```
Output:
```plaintext theme={null}
NAME READY STATUS RESTARTS AGE
frontend-deployment-7f8dcd896-stmbx 0/1 ImagePullBackOff 0 59s
frontend-deployment-7f8dcd896-zc6wc 0/1 ErrImagePull 0 59s
frontend-deployment-7f8dcd896-jgcbx 0/1 ErrImagePull 0 59s
frontend-deployment-7f8dcd896-jbr44 0/1 ErrImagePull 0 59s
```
None of the four pods are ready. To investigate further, inspect one of the pods in detail:
```bash theme={null}
kubectl describe pod frontend-deployment-7f8dcd896-stmbx
```
Within the detailed output, you will notice that the image used is "busybox888" (visible under the “Pulling image” events). Key excerpts from the `describe` output include:
```plaintext theme={null}
State: Waiting
Reason: ErrImagePull
...
Pulling image "busybox888"
Warning Failed ... Failed to pull image "busybox888": rpc error: code = Unknown desc = failed to pull and unpack image "docker.io/library/busybox888:latest": pull access denied, repository does not exist or may require authorization: server response: authorization failed
Warning Failed ... Error: ErrImagePull
Normal BackOff ... Back-off pulling image "busybox888"
```
The image "busybox888" does not exist, which is why the pods are not becoming ready. Verify and update your image name as needed.
***
## Creating a Deployment Using a YAML Definition
The next task is to create a new deployment using a YAML file. In your root directory, verify the YAML file presence:
```bash theme={null}
controlplane ~ pwd
/root
controlplane ~ ls
deployment-definition-1.yaml sample.yaml
```
Then, attempt to create the deployment by executing:
```bash theme={null}
kubectl create -f deployment-definition-1.yaml
```
You might encounter an error similar to this:
```plaintext theme={null}
Error from server (BadRequest): error when creating "deployment-definition-1.yaml": deployment in version "v1" cannot be handled as a Deployment: no kind "deployment" is registered for version "apps/v1" in scheme "k8s.io/apimachinery/v1.23.3-k3s1/pkg/runtime/schema.go:100"
```
Upon inspecting the file, you could notice that although the API version is correctly set to `apps/v1`, the kind is mistakenly written in lowercase. The `kind` field is case sensitive and must start with an uppercase letter.
Below is the corrected YAML definition:
```yaml theme={null}
apiVersion: apps/v1
kind: Deployment
metadata:
name: deployment-1
spec:
replicas: 2
selector:
matchLabels:
name: busybox-pod
template:
metadata:
labels:
name: busybox-pod
spec:
containers:
- name: busybox-container
image: busybox888
command:
- sh
- "-c"
- echo Hello Kubernetes! && sleep 3600
```
After correcting the `kind` field, save the file and run:
```bash theme={null}
kubectl create -f deployment-definition-1.yaml
```
If the file is corrected properly, the deployment will be created successfully.
***
## Creating a Deployment via the Command Line
An alternative method is to create a deployment directly from the command line by specifying the name, image, and number of replicas. For example, to create an HTTP frontend deployment with three replicas using a specific image, run:
```bash theme={null}
kubectl create deployment http-frontend --image= --replicas=3
```
It is a good practice to verify the newly created deployment immediately:
```bash theme={null}
kubectl get deploy
```
You should see the new `http-frontend` deployment listed, and eventually, the pods should transition to a ready state.
***
## Summary
This lesson demonstrated how to:
* Check the environment for existing pods, ReplicaSets, and deployments.
* Troubleshoot a deployment issue caused by an incorrect image.
* Correctly create a deployment using a YAML definition.
* Create a deployment directly from the command line.
Ensuring correct syntax and case sensitivity in your Kubernetes YAML files is crucial to avoid deployment errors.
By following these steps, you will strengthen your understanding of Kubernetes deployments and develop the skills to quickly troubleshoot and resolve common issues.