Docker Swarm

Prerequisites:

• Docker should be installed on all the nodes (manager and workers).
• Nodes should be able to communicate with each other over the network.

Step 1

Initialize Docker Swarm on the Manager Node

Log in to the manager node and run the following command in the terminal:

docker swarm init

This command initializes Docker Swarm on the manager node, and it will also generate a token that you can use to join worker nodes to the cluster.

Step 2

Join Worker Nodes to the Swarm

After running the docker swarm init command on the manager node, it will output a command to join other nodes to the swarm. It will look something like this:

docker swarm join — token <SWARM_TOKEN> <MANAGER_IP>:2377

Run it on each worker node you want to add to the cluster.

Step 3

Check the Swarm Status

To check the status of your Docker Swarm and view the nodes in the cluster, run the following command on the manager node:

docker node ls

This command will display a list of nodes in the swarm along with their status and availability.

Step 4

Deploy Services on the Swarm

With Docker Swarm set up, you can now deploy services to the cluster. A service defines how a container should run in the cluster.

For example, let’s deploy a simple Nginx web server service:

docker service create — replicas 3 -p 80:80 — name webserver nginx

This command will create a service called “webserver” with three replicas (three instances) of the Nginx container, and it will publish port 80 to the host.

Step 5

Scale the Service

You can easily scale the service up or down using the docker service scale command. For example, to scale the “webserver” service to five replicas, run:

docker service scale webserver=5

Step 6

Update the Service

If you need to update the service, you can use the docker service update command. For example, to change the number of replicas to ten, run:

docker service update — replicas 10 webserver

Step 7

Remove the Service

When you no longer need the service, you can remove it with the following command:

docker service rm webserver

Step 8

Leave the Swarm

If you want to remove a node from the swarm, run the following command on the node you want to remove:

docker swarm leave

If the node is a manager, use docker swarm leave — force to force it to leave.

These are the basic steps to set up and use Docker Swarm to create a simple cluster. Docker Swarm provides many more features, such as overlay networks, secrets management, rolling updates, and more, which can be explored as you get more familiar with it.