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Containerization & Orchestration/Kubernetes/workloads/03-Replicaset.md

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+# 🧩 Kubernetes ReplicaSet Management
+
+A guide to working with **ReplicaSets** in Kubernetes, including inspection, editing behavior, and configuration examples.
+
+---
+
+## 📦 Listing Pods and ReplicaSets
+
+### 🔹 List Pods in a Namespace
+
+```bash
+kubectl get pod -n <namespace>
+```
+
+### 🔹 List ReplicaSets in a Namespace
+
+```bash
+kubectl get rs -n <namespace>
+```
+
+---
+
+## ✏️ Editing a ReplicaSet
+
+You can attempt to edit a ReplicaSet:
+
+```bash
+kubectl edit rs -n <namespace> <replica-set-name>
+```
+
+> ⚠️ **Note:**
+> Editing the **image** in a ReplicaSet directly will not automatically update existing Pods.
+> This is because ReplicaSets do not perform **rolling updates**.
+> Pods will only use the new image **after the old ones are deleted and new ones are created**.
+
+**To apply image changes effectively:**
+
+1. **Delete existing Pods** manually:
+
+   ```bash
+   kubectl delete pod -l <label-selector> -n <namespace>
+   ```
+
+2. **Or**, use a higher-level controller like a **Deployment** for image updates and rolling behavior.
+
+---
+
+## 🧾 Example ReplicaSet YAML
+
+Below is a minimal and clear ReplicaSet configuration:
+
+```yaml
+apiVersion: apps/v1
+kind: ReplicaSet
+metadata:
+  name: app-1
+  namespace: dev
+  labels:
+    label1: test1
+    app.kubernetes.io/label2: test2
+spec:
+  replicas: 3
+  selector:
+    matchLabels:
+      app.kubernetes.io/label2: test2
+  template:
+    metadata:
+      labels:
+        app.kubernetes.io/label2: test2
+        os: linux
+    spec:
+      containers:
+        - name: nginx
+          image: nginx
+```
+
+> ✅ **Tip:**
+> Ensure that the `template.metadata.labels` **matches exactly** with `spec.selector.matchLabels`.
+> This is critical for proper ReplicaSet Pod matching.
+