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Containerization-Orchestration/Docker/5-Docker-Swarm.md

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+# 📦 Docker Swarm Documentation
+
+Comprehensive guide to managing a **Docker Swarm** cluster. This document includes core commands, workflows, and best practices for maintaining a healthy and operational environment.
+
+---
+
+## 📚 Table of Contents
+
+1. [🔧 Cluster Health & Manager Count](#-cluster-health--manager-count)
+2. [🚀 Example Workflow: Setting Up Nginx](#-example-workflow-setting-up-nginx)
+3. [⚙️ Cluster Initialization and Management](#️-cluster-initialization-and-management)
+4. [🖥️ Node Management](#️-node-management)
+5. [🛠️ Service Management](#️-service-management)
+6. [🔑 Join Tokens & Node Configuration](#-join-tokens--node-configuration)
+
+---
+
+## 🔧 Cluster Health & Manager Count
+
+A Docker Swarm cluster requires a **majority of manager nodes** to be functional for quorum.
+
+> **Best Practice:** Always maintain **more than 50%** manager nodes online. Losing quorum will render the cluster non-operational.
+
+---
+
+## 🚀 Example Workflow: Setting Up Nginx
+
+Docker Swarm handles service deployment through several internal components:
+
+1. **API** – Receives service requests.
+2. **Allocator** – Determines resource allocation.
+3. **Dispatcher** – Assigns tasks to nodes.
+4. **Scheduler** – Places tasks on optimal nodes.
+
+This process ensures resilient and efficient service distribution.
+
+---
+
+## ⚙️ Cluster Initialization and Management
+
+### 🔹 Initialize Cluster
+
+```bash
+docker swarm init
+```
+
+### 🔹 Initialize with Specific Interface
+
+```bash
+docker swarm init --advertise-addr <ip-or-interface>
+```
+
+### 🔹 Join Existing Cluster
+
+```bash
+docker swarm join
+```
+
+### 🔹 Leave Cluster
+
+```bash
+docker swarm leave
+```
+
+### 🔹 Unlock a Manager Node
+
+```bash
+docker swarm unlock
+```
+
+---
+
+## 🖥️ Node Management
+
+### 🔸 List Nodes
+
+```bash
+docker node ls
+```
+
+**Example Output:**
+
+```
+ID                            HOSTNAME   STATUS    AVAILABILITY   MANAGER STATUS   ENGINE VERSION
+8yw8jrjeqczaci0qkuy060g09 *   docker-1   Ready     Active         Leader           24.0.5
+v4gvf7xenw0izmxgvhr6hb2rj     docker-2   Ready     Active                          24.0.5
+kd3ujmt1ey3pw6v9189fouxfa     docker-3   Ready     Active         Reachable        24.0.5
+tm1msy58ztcltt36rs1lb76p7     docker-4   Down      Active                          24.0.5
+```
+
+### 🔸 Remove a Node
+
+```bash
+docker node rm <node-id>
+```
+
+### 🔸 Promote to Manager
+
+```bash
+docker node promote <hostname-or-id>
+```
+
+### 🔸 Inspect a Node
+
+```bash
+docker node inspect <nodename>
+```
+
+### 🔸 Change Node Role
+
+```bash
+docker node update --role manager <nodename>
+docker node update --role worker <nodename>
+```
+
+### 🔸 Change Node Availability
+
+```bash
+docker node update --availability active <nodename>
+docker node update --availability pause <nodename>
+docker node update --availability drain <nodename>
+```
+
+### 🔸 Add or Remove Labels
+
+**Add:**
+
+```bash
+docker node update --label-add env=development <nodename>
+docker node update --label-add env=testing <nodename>
+```
+
+**Remove:**
+
+```bash
+docker node update --label-rm env= <nodename>
+docker node update --label-rm env <nodename>
+```
+
+**Use label constraints in service deployment:**
+
+```yaml
+deploy:
+  placement:
+    constraints:
+      - node.labels.env == development
+```
+
+---
+
+## 🛠️ Service Management
+
+### 🔹 Show Tasks on a Node
+
+```bash
+docker node ps
+```
+
+### 🔹 List All Services
+
+```bash
+docker service ls
+```
+
+### 🔹 Create a New Service
+
+```bash
+docker service create --name <service-name> <image-name>
+```
+
+### 🔹 Scale a Service
+
+```bash
+docker service scale <service-name>=<replica-count>
+```
+
+**Example:**
+
+```bash
+docker service scale nginx=5
+```
+
+### 🔹 Inspect a Service
+
+```bash
+docker service inspect <service-name>
+```
+
+### 🔹 Create Service with Replicas, Env Vars, and Port Mapping
+
+```bash
+docker service create \
+  --name <service-name> \
+  --replicas <count> \
+  --env <ENV_VAR=value> \
+  --publish <host-port>:<container-port> \
+  <image-name>
+```
+
+**Example:**
+
+```bash
+docker service create \
+  --name nginx \
+  --replicas 3 \
+  --env MY_ENV_VAR=value \
+  --publish 8080:80 \
+  nginx
+```
+
+---
+
+## 🔑 Join Tokens & Node Configuration
+
+Securely add nodes to your Swarm using join tokens.
+
+### 🔹 Get Worker Token
+
+```bash
+docker swarm join-token worker
+```
+
+### 🔹 Get Manager Token
+
+```bash
+docker swarm join-token manager
+```
+