Working with Docker Swarm Mode

1. Initializing Swarm

Command	Description	Notes
docker swarm init	Initializes a new swarm	Must be run on the manager node
docker swarm init --advertise-addr <ip>	Initializes swarm with specific IP address	Useful for multi-host environments
docker swarm init --listen-addr <ip>	Specifies the address to listen on	Defaults to 0.0.0.0:2377

Example: Initializing a Docker Swarm

docker swarm init

Note: The docker swarm init command returns a join token that is used to add worker nodes to the swarm.

2. Joining Swarm as Worker

Option	Values	Description
docker swarm join-token worker	`docker swarm join-token worker`	Generates the join token for worker nodes

Example: Joining a Worker Node

docker swarm join --token SWMTKN-1-xxx<REDACTED> xxx.xxx.xxx.xxx:2377

Note: The join token is valid for 24 hours by default. After that, a new token must be generated.

3. Joining Swarm as Manager

Option	Values	Description
docker swarm join-token manager	`docker swarm join-token manager`	Generates a token to join new managers to the swarm

Example: Joining a Manager Node

# On the manager node, generate a join token
docker swarm join-token manager

# Output will look like:
#   docker swarm join --token SWMTKN-1-xxx...yyy 192.168.1.10:2377

# On the new manager node, run:
docker swarm join --token SWMTKN-1-xxx...yyy 192.168.1.10:2377

Note: The join token is valid for 24 hours by default. Managers can be added to the swarm using the generated token.

4. Listing Swarm Nodes

Command	Description	Options	Example
docker node ls	List all nodes in the swarm	`--format`, `--filter`	`docker node ls`
docker node ls --format json	Output in JSON format	`--format`	`docker node ls --format json`
docker node ls --filter role=manager	Filter nodes by role	`--filter`	`docker node ls --filter role=manager`

Note: The docker node ls command lists all nodes in the swarm, including their status, availability, and roles.

5. Inspecting Nodes

Property	Description	Example
docker node ls	List all nodes in the swarm	`docker node ls`
docker node inspect <node-id>	Inspect a specific node	`docker node inspect node-1`
docker node ps <node-id>	List tasks running on a specific node	`docker node ps node-1`

Example: Inspecting a Node

docker node inspect node-1

Note: The output includes detailed information about the node's configuration, status, and resource usage.

6. Promoting Worker to Manager

Command	Description	Notes
docker node promote <node-id>	Promotes a worker node to a manager node	Requires swarm mode to be active

Example: Promoting a Worker Node

docker node promote worker-1

Note: The node must be in a healthy state to be promoted.

Warning: Promoting a node increases the number of managers in the swarm, which can impact performance and fault tolerance.

7. Demoting Manager to Worker

Command	Description	Notes
docker node demote <node-id>	Demotes a manager node to a worker node	Must be run from a manager node or with appropriate permissions

Example: Demoting a Manager Node

docker node demote manager-01

Note: Ensure that the cluster has sufficient worker nodes to maintain desired availability and redundancy after demotion.

8. Updating Swarm Configuration

Configuration Option	Description	Default Value	Notes
dockerd --config-file	Path to the JSON configuration file for Docker daemon	`/etc/docker/daemon.json`	Used to configure Docker daemon settings
--data-root	Root directory for Docker data storage	`/var/lib/docker`	Must be accessible to all nodes in the swarm
--log-driver	Default logging driver for containers	`json-file`	Can be overridden per container
--log-opts	Options for the logging driver	`null`	Example: `max-size=10m`

Example: Updating Docker Daemon Configuration

{
  "log-driver": "syslog",
  "log-opts": {
    "syslog-address": "tcp://localhost:514",
    "syslog-facility": "local0"
  },
  "data-root": "/mnt/docker-data"
}

Note: Changes to the Docker daemon configuration require a restart of the Docker service on each node in the swarm.

Warning: Modifying data-root requires careful handling to ensure all nodes can access the new location.

9. Managing Join Tokens

Token Type	Description	Command	Notes
manager	Token for joining new manager nodes	`docker swarm join-token manager`	Used to securely add new manager nodes to the swarm
worker	Token for joining new worker nodes	`docker swarm join-token worker`	Used to securely add new worker nodes to the swarm

Example: Generate a new join token for workers

docker swarm join-token worker

Example: Use a join token to add a worker node

docker swarm join --token SWMTKN-1-xxx worker-node-ip:2377

Note: Join tokens are valid for 12 hours by default. After that, they must be regenerated.

10. Removing Node from Swarm

Command	Description	Notes
docker node rm <node-id>	Removes a node from the swarm	Must be run on a manager node
docker node rm --force <node-id>	Forcefully removes a node from the swarm	Useful for unreachable nodes

Example: Removing a Node

# Remove a node from the swarm
docker node rm worker-01

# Force remove an unreachable node
docker node rm --force worker-01

Note: Before removing a node, ensure that its services are either replicated or stopped to avoid service disruption.

11. Leaving Swarm

Command	Description	Notes
docker swarm leave	Leave the swarm	Runs on worker nodes to leave the swarm. If node is a manager, use `--force` to leave without removing the swarm.
docker swarm leave --force	Force leave the swarm	Used to leave the swarm even if the node is a manager. This removes the node from the swarm and resets it to a standalone Docker daemon.

Example: Leaving a Swarm

docker swarm leave

Example: Force Leaving a Swarm

docker swarm leave --force

Note: After leaving the swarm, the node becomes a standalone Docker daemon and will no longer participate in swarm operations.

12. Configuring Swarm Encryption

Configuration Option	Description	Default Value	Notes
--encryption-key	Encryption key for swarm communication	None	Required for enabling encryption
--auto-encrypt	Enable automatic encryption of swarm communication	false	Can be set to true to enable automatic encryption

Example: Enabling Swarm Encryption

docker swarm init --auto-encrypt

Note: The encryption key must be securely stored and managed to ensure the security of the swarm.

Warning: If encryption is enabled, all nodes in the swarm must have access to the encryption key.