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Containerization & Orchestration/Docker/5-Docker-Swarm.md Executable file
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# Docker Swarm Documentation
This guide covers key commands and workflows for managing a Docker Swarm cluster. It includes information on initializing the cluster, node management, service management, and best practices to ensure your cluster remains operational.
---
## 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](#join-tokens)
---
## Cluster Health & Manager Count
To maintain a healthy and functional Docker Swarm cluster, **the number of manager nodes must exceed 50% of the total nodes**. If the manager nodes fall below 51% of the cluster, the system will lose quorum and become non-operational. Always monitor your manager count to ensure high availability.
---
## Example Workflow: Setting Up Nginx
When deploying services such as Nginx, the typical workflow in Docker Swarm is:
1. **API**: Handle incoming requests.
2. **Allocator**: Distribute workload to available nodes.
3. **Dispatcher**: Manage task assignments.
4. **Scheduler**: Ensure tasks run on the optimal nodes.
This workflow ensures that your service is efficiently distributed and scaled across the cluster.
---
## Cluster Initialization and Management
### Create Cluster
Initialize a new Docker Swarm cluster:
```bash
docker swarm init
```
This command sets up the current node as the manager of a new cluster.
### Create Cluster with a Specific Interface
Specify an IP address or interface name when initializing the cluster:
```bash
docker swarm init --advertise-addr <ip or interface name>
```
This ensures that the node advertises the correct network interface for other nodes to join.
### Join Cluster
Add a node to an existing Docker Swarm cluster:
```bash
docker swarm join
```
### Leave Cluster
Remove a node from the cluster:
```bash
docker swarm leave
```
### Unlock Locked Manager
Unlock a manager node that has been locked:
```bash
docker swarm unlock
```
---
## Node Management
### List Nodes
View the status and details of all nodes in your cluster:
```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 Node
Remove a node from the cluster by specifying its ID:
```bash
docker node rm <node-id>
```
**Example:**
```bash
docker node rm tm1msy58ztcltt36rs1lb76p7
```
### Promote Node to Manager
Upgrade a worker node to a manager node:
```bash
docker node promote <hostname or ID>
```
**Example:**
```bash
docker node promote v4gvf7xenw0izmxgvhr6hb2rj
```
This command promotes the specified node, enabling it to participate in cluster management decisions.
---
## Service Management
### Show Task Status on Cluster
Display the status of tasks running on each node:
```bash
docker node ps
```
### List Services
List all services currently running in the cluster:
```bash
docker service ls
```
### Create Service
Create a new service with the specified name and Docker image:
```bash
docker service create --name <service-name> <image-name>
```
### Scale Service
Adjust the number of replicas for an existing service:
```bash
docker service scale <service-name>=<replica-count>
```
**Example:**
```bash
docker service scale nginx=5
```
This command scales the `nginx` service to 5 replicas.
### Inspect Service
View detailed information about a specific service:
```bash
docker service inspect <service-name>
```
### Create Service with Replicas and Environment Variables
Launch a new service with multiple replicas, environment variables, and port publishing:
```bash
docker service create --name <service-name> --replicas <replica-count> --env <env-variable> --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
```
This creates an `nginx` service with 3 replicas, sets the environment variable `MY_ENV_VAR` to `value`, and maps port 8080 on the host to port 80 in the container.
---
## Join Tokens
To securely add new nodes to the swarm, use the join tokens provided by Docker Swarm.
### Get Worker Join Token
Display the token required for a node to join as a worker:
```bash
docker swarm join-token worker
```
### Get Manager Join Token
Display the token required for a node to join as a manager:
```bash
docker swarm join-token manager
```

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# Docker Swarm Documentation
## Manager Count
To ensure the cluster remains functional, the number of manager nodes must be more than 50%. If it falls below 51%, the cluster will become non-operational.
## Example: Setting Up Nginx
**Workflow:** API → Allocator → Dispatcher → Scheduler
## Commands
### Cluster Initialization and Management
- **Create Cluster**
```bash
docker swarm init
```
Initializes a new Docker Swarm cluster.
- **Join Cluster**
```bash
docker swarm join
```
Joins a node to an existing Docker Swarm cluster.
- **Create Cluster with Specific Interface**
```bash
docker swarm init --advertise-addr <ip or interface name>
```
Initializes a new Docker Swarm cluster, specifying the IP or interface name to advertise.
- **Leave Cluster**
```bash
docker swarm leave
```
Removes a node from the Docker Swarm cluster.
- **Unlock Locked Manager**
```bash
docker swarm unlock
```
Unlocks a locked manager node in the Docker Swarm cluster.
### Node Management
- **List Nodes**
```bash
docker node ls
```
Displays information about the nodes in the cluster.
**Example Output:**
```bash
docker node ls
```
```
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-3 Down Active 24.0.5
```
- **Remove Node**
```bash
docker node rm <node-id>
```
Removes a node from the cluster.
**Example:**
```bash
docker node rm tm1msy58ztcltt36rs1lb76p7
```
- **Promote Node to Manager**
```bash
docker node promote <hostname or ID>
```
Promotes a worker node to a manager node.
**Example:**
```bash
root@docker-1:~# docker node promote v4gvf7xenw0izmxgvhr6hb2rj
Node v4gvf7xenw0izmxgvhr6hb2rj promoted to a manager in the swarm.
```
### Service Management
- **Show Task Status on Cluster**
```bash
docker node ps
```
Displays the status of tasks running on nodes in the cluster.
- **List Services**
```bash
docker service ls
```
Lists all services running in the cluster.
- **Create Service**
```bash
docker service create --name <service-name> <image-name>
```
Creates a new service with the specified name and image.
- **Scale Service**
```bash
docker service scale <service-name>=<replica-count>
```
Scales the number of replicas for a service.
**Example:**
```bash
docker service scale nginx=5
```
Scales the `nginx` service to 5 replicas.
- **Inspect Service**
```bash
docker service inspect <service-name>
```
Displays detailed information about a service.
- **Create Service with Replicas and Environment Variables**
```bash
docker service create --name <service-name> --replicas <replica-count> --env <env-variable> <image-name>
```
Creates a new service with the specified name, number of replicas, and environment variables.
**Example:**
```bash
docker service create --name nginx --replicas 3 --env MY_ENV_VAR=value nginx
```
Creates an `nginx` service with 3 replicas and an environment variable `MY_ENV_VAR` set to `value`.