How to Join a Docker Swarm Worker Node

Joining a Docker Swarm worker node is a critical task for anyone managing a Docker environment. This article will walk you through the detailed steps and commands required to switch your current Docker Engine into swarm mode, request a TLS certificate from the manager, and join the node to a swarm based on the provided token. Understanding these steps will ensure that your worker nodes are seamlessly integrated into a Docker Swarm cluster, enhancing your container orchestration capabilities.

Switching Docker Engine to Swarm Mode

The first step in integrating a new node into a Docker Swarm cluster is to switch the Docker Engine on the current node into swarm mode. This can be done using the following command:

sudo docker swarm init

This command initiates the swarm mode and generates a token that is required to join other nodes to the cluster. The output will look something like this:

Swarm initialized: current node(node_id) is now a manager.
To add a worker to this swarm, run the following command:
    node_ip:2377 --token token

Remember to save the token as you will need it to join worker nodes later.

Requesting a TLS Certificate from the Manager

For enhanced security in a Docker Swarm environment, it is recommended to use TLS certificates. To request a TLS certificate from the manager, follow these steps:

Ensure that your Docker Engine is running in swarm mode as described above.

Generate a CA certificate using OpenSSL. The command below creates a CA certificate:

openssl req -newkey rsa:2048 -nodes -keyout ca-key -x509 -days 365 -out ca-cert

Create a certificate signing request (CSR) for each node. Use the following command to create a CSR for a worker node:

openssl req -newkey rsa:2048 -nodes -keyout node-key -out node-csr

Sign the CSR with your CA certificate to generate a TLS certificate. The command to sign the CSR is:

openssl x509 -req -in node-csr -CA ca-cert -CAkey ca-key -CAcreateserial -out node-cert -days 365 -extfile csr_extension_file

Ensure that the CSR extension file contains the necessary configuration to properly sign the certificate.

Install the generated TLS certificate on the worker node using:

sudo cp node-cert 
sudo cp node-key 

After completing these steps, all nodes in your swarm will be able to communicate securely using TLS.

Joining the Current Node to the Swarm

To join a worker node to the swarm, you need to use the docker swarm join command with the appropriate options. The following steps guide you through this process:

Retrieve the swarm join command from the manager node by running:

sudo docker swarm join-token worker -q

Copy the join command to the worker node and run it. The command should include the IP address of the manager node and the generated token.

Once the worker node completes this process, it will be successfully added to the Docker Swarm cluster.

Conclusion

Joining a worker node to a Docker Swarm cluster is a straightforward process once you understand the necessary steps and commands. By switching the Docker Engine into swarm mode, requesting TLS certificates, and executing the join command with the proper token, you can seamlessly integrate new nodes into your Docker Swarm environment, enhancing scalability, reliability, and security. Use these detailed instructions to ensure that your worker nodes are fully operational and contributing to the overall performance of your Docker Swarm cluster.

Frequently Asked Questions

Q: What is Docker Swarm?

Docker Swarm is a native clustering system for Docker. It allows you to turn a group of Docker nodes into a single Virtual Docker Swarm for easy management and orchestration. Swarm lets you run applications across multiple managed hosts, thereby scaling and ensuring the reliability of your containerized applications.

Q: What is a Docker Worker Node?

A Docker worker node is a node that can run Docker containers within a Docker Swarm. It can be added to an existing Docker Swarm cluster to increase the capacity and improve the performance of your application by running containers across multiple worker nodes.

Q: Why is SSL/TLS important in a Docker Swarm?

Using SSL/TLS is crucial for secure communication between Docker nodes in the swarm. It ensures that data transmitted between nodes is protected from eavesdropping and tampering, thereby enhancing the security and reliability of your Docker Swarm cluster.