> ## 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.

# Deployments

> This article explains Kubernetes Deployments, covering their features, how they manage resources, and how to create and inspect Deployment manifests.

Kubernetes Deployments automate application upgrades, scaling, and self-healing in production environments. They enable rolling updates, controlled rollbacks, and pause/resume capabilities—all without downtime. In this guide, you’ll learn how Deployments manage ReplicaSets and Pods, define a Deployment manifest, and inspect your resources using `kubectl`.

## Why Use a Deployment?

* **Rolling Updates**: Replace pods one by one to avoid service interruption.
* **Rollbacks**: Instantly revert to a previous version if something goes wrong.
* **Pause & Resume**: Apply several changes as a batch and resume when ready.
* **Declarative Scaling**: Increase or decrease replicas in your manifest.

## How Deployments Work

A Deployment sits above ReplicaSets and Pods:

1. **Pod**: The basic execution unit (one or more containers).
2. **ReplicaSet**: Ensures a specified number of pod replicas run at any time.
3. **Deployment**: Manages ReplicaSets and orchestrates updates, rollbacks, and scaling.

<Frame>
  ![The image illustrates a Kubernetes deployment structure, showing a deployment with multiple pods and a replica set, along with versioning and control icons.](https://kodekloud.com/kk-media/image/upload/v1752873996/notes-assets/images/Docker-Certified-Associate-Exam-Course-Deployments/kubernetes-deployment-pods-replica-set.jpg)
</Frame>

## Resource Comparison

| Resource Type | Purpose                                   | Example Command                               |
| ------------- | ----------------------------------------- | --------------------------------------------- |
| Pod           | Single instance of one or more containers | `kubectl run nginx --image=nginx`             |
| ReplicaSet    | Maintains desired pod replicas            | `kubectl create -f replicaset-definition.yml` |
| Deployment    | Declarative updates and rollbacks         | `kubectl apply -f deployment-definition.yml`  |

## Writing a Deployment Manifest

Create a YAML file (`deployment-definition.yml`) to declare your desired state:

```yaml theme={null}
apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp-deployment
  labels:
    app: myapp
    type: front-end
spec:
  replicas: 3
  selector:
    matchLabels:
      type: front-end
  template:
    metadata:
      labels:
        app: myapp
        type: front-end
    spec:
      containers:
        - name: nginx-container
          image: nginx:latest
          ports:
            - containerPort: 80
```

* **apiVersion**: The API group (`apps/v1`).
* **kind**: Must be `Deployment`.
* **metadata**: Identifies the Deployment (`name` and `labels`).
* **spec.replicas**: Desired number of pods.
* **spec.selector**: Matches labels on pods.
* **spec.template**: Defines the pod spec, just like a ReplicaSet.

<Callout icon="lightbulb" color="#1CB2FE">
  Using `kubectl apply -f` is recommended for idempotent updates. It creates or updates resources based on your manifest.
</Callout>

## Deploying and Inspecting Resources

1. **Create or update the Deployment**
   ```bash theme={null}
   kubectl apply -f deployment-definition.yml
   ```
2. **View Deployments**
   ```bash theme={null}
   kubectl get deployments
   ```
   Example output:
   ```text theme={null}
   NAME              READY   UP-TO-DATE   AVAILABLE   AGE
   myapp-deployment  3/3     3            3           30s
   ```
3. **List ReplicaSets**
   ```bash theme={null}
   kubectl get rs
   ```
4. **Check Pods**
   ```bash theme={null}
   kubectl get pods
   ```
5. **See All Resources**
   ```bash theme={null}
   kubectl get all
   ```

<Callout icon="triangle-alert" color="#FF6B6B">
  If an update fails, rollback immediately:

  ```bash theme={null}
  kubectl rollout undo deployment/myapp-deployment
  ```
</Callout>

## Next Steps & References

* Learn more about [Kubernetes Deployments](https://kubernetes.io/docs/concepts/workloads/controllers/deployment/)
* Explore the [kubectl Cheat Sheet](https://kubernetes.io/docs/reference/kubectl/cheatsheet/)
* Official [Kubernetes Documentation](https://kubernetes.io/docs/)

<CardGroup>
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