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Containerization-Orchestration/Kubernetes/workloads/11-Config-map.md

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+# 🧾 Kubernetes ConfigMap Guide
+
+Manage configuration without hardcoding! `ConfigMaps` let you store external configurations as key-value pairs and inject them into Kubernetes workloads.
+
+---
+
+## 📘 What is a ConfigMap?
+
+A **ConfigMap** is a Kubernetes object used to store **non-confidential configuration data** in **key-value** format. You can:
+
+* 📄 Mount it as files inside a Pod
+* 🌿 Use it as environment variables
+* 🧩 Keep your container images decoupled from configuration
+
+---
+
+## ⚙️ Creating a ConfigMap
+
+You can create a ConfigMap from files or directories:
+
+```bash
+kubectl -n <namespace> create configmap <configmap-name> --from-file=<file-or-directory>
+```
+
+### ✅ Examples
+
+```bash
+# From a single file
+kubectl -n <ns> create configmap nginx-conf --from-file=./nginx.conf
+
+# From multiple files
+kubectl -n <ns> create configmap nginx-conf \
+  --from-file=./nginx.conf \
+  --from-file=./site.conf
+```
+
+---
+
+## 📂 Viewing & Editing ConfigMaps
+
+```bash
+# List all ConfigMaps in a namespace
+kubectl get cm -n <namespace>
+
+# View detailed ConfigMap info
+kubectl describe configmap <name> -n <namespace>
+
+# Edit in-place
+kubectl -n <namespace> edit configmap <configmap-name>
+```
+
+---
+
+## 📄 YAML: ConfigMap Example
+
+```yaml
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: game-demo
+data:
+  player_initial_lives: "3"
+  ui_properties_file_name: "user-interface.properties"
+
+  game.properties: |
+    enemy.types=aliens,monsters
+    player.maximum-lives=5    
+
+  user-interface.properties: |
+    color.good=purple
+    color.bad=yellow
+    allow.textmode=true    
+```
+
+---
+
+## 💡 Usage Examples
+
+### 📌 ConfigMap as Environment Variables
+
+**ConfigMap:**
+
+```yaml
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: app-config
+  namespace: default
+data:
+  APP_MODE: "production"
+  LOG_LEVEL: "info"
+  FEATURE_FLAG_X: "enabled"
+```
+
+**Pod:**
+
+```yaml
+apiVersion: v1
+kind: Pod
+metadata:
+  name: my-app
+spec:
+  containers:
+    - name: my-container
+      image: busybox
+      command: ["/bin/sh", "-c", "env && sleep 3600"]
+      envFrom:
+        - configMapRef:
+            name: app-config
+```
+
+---
+
+### 🧾 Mounting ConfigMap as a File (nginx.conf example)
+
+**ConfigMap:**
+
+```yaml
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: nginx-config
+  namespace: default
+data:
+  nginx.conf: |
+    worker_processes  1;
+
+    events {
+        worker_connections  1024;
+    }
+
+    http {
+        include       mime.types;
+        default_type  application/octet-stream;
+
+        sendfile        on;
+        keepalive_timeout  65;
+
+        server {
+            listen       80;
+            server_name  localhost;
+
+            location / {
+                root   /usr/share/nginx/html;
+                index  index.html index.htm;
+            }
+
+            error_page   500 502 503 504  /50x.html;
+            location = /50x.html {
+                root   /usr/share/nginx/html;
+            }
+        }
+    }
+```
+
+**Pod:**
+
+```yaml
+apiVersion: v1
+kind: Pod
+metadata:
+  name: nginx-pod
+spec:
+  containers:
+    - name: nginx
+      image: nginx:latest
+      volumeMounts:
+        - name: nginx-config-volume
+          mountPath: /etc/nginx/nginx.conf
+          subPath: nginx.conf
+  volumes:
+    - name: nginx-config-volume
+      configMap:
+        name: nginx-config
+```
+
+---
+
+## 🛠 Pro Tips
+
+* 🔐 For **sensitive data**, use **Secrets** instead of ConfigMaps.
+* 🧪 Combine ConfigMaps with **Deployment** objects for flexible, versioned config management.
+* 📦 Use `--from-env-file` to load multiple key-value pairs from a `.env` style file:
+
+  ```bash
+  kubectl create configmap my-config --from-env-file=env.list
+  ```
+