How to install Docker Swarm cluster on Debian 10

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Docker Swarm is a tool for orchestrating Docker hosts. We can create highly available and high-performance Docker clusters and distribute applications among hosts.

Docker swam uses a manager host and worker node architecture. You can have one or more Manager nodes in your docker swarm cluster. The manager node uses the native Docker API and shares the database of the Docker Swarm cluster with the auxiliary nodes. The manager host maintains the cluster state, schedules tasks, and handles HTTP API endpoints.

A worker node is an instance of the Docker engine that executes the container.

Compared with Kubernetes which has complete functions such as monitoring, entry and volume, Docker swarm has a simpler status. Docker Swarm also lacks automatic expansion capabilities, so containers cannot be automatically expanded based on monitoring and resource utilization. You must manually scale the container.

This guide will discuss how to set up a Docker Swarm cluster on a Debian 10 host.

Step 1-Node preparation

Configure the host name for each node in the host /etc/hosts Used for local resolution files.

sudo vim /etc/hosts

Add detailed information about the nodes on each server, including the manager node and the auxiliary node.

10.31.45.182	manager
10.31.45.226    worker-01
10.31.45.219    worker-02

Ensure that the hosts can reach each other through ping.

Step 2-Install Docker CE on Debian 10

We need to install the Docker engine on all hosts, managers and secondary nodes.

Install the dependency package on the host:

sudo apt-get update
sudo apt-get install apt-transport-https ca-certificates curl gnupg-agent software-properties-common

Add the Docker GPG key:

curl -fsSL https://download.docker.com/linux/debian/gpg | sudo apt-key add -

Add the Docker repository:

sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/debian $(lsb_release -cs) stable"

Install Docker engine

sudo apt-get update
sudo apt-get install docker-ce docker-ce-cli

Start and enable Docker

sudo systemctl start docker
sudo systemctl enable docker

Add your user to the Docker group

sudo usermod -aG docker ${USER}

Step 3-Initialize the Docker Swarm cluster

In this step, we need to initialize the Docker cluster mode on the manager node, and then we can add worker nodes later.

The following command is used to initialize Docker Swarm Manager.You should replace Use the IP address of your administrator node.

newgrp docker
sudo docker swarm init --advertise-addr <manager-IP>

Sample output:

$ docker swarm init --advertise-addr 10.31.45.182

Swarm initialized: current node (xj5sqdpsbs5x2pgt670dft31m) is now a manager.

To add a worker to this swarm, run the following command:

    docker swarm join --token SWMTKN-1-5yat7zlum78qmnlhv1vs0b0k4c42jafh5kt8xtb36eara4c5ip-490dr4yhpbe5qnic476wh90zg 10.31.45.182:2377

To add a manager to this swarm, run 'docker swarm join-token manager' and follow the instructions.

After initializing the manager node, we can now add worker nodes using the connection token provided in the example above.

$ docker swarm join --token SWMTKN-1-5yat7zlum78qmnlhv1vs0b0k4c42jafh5kt8xtb36eara4c5ip-490dr4yhpbe5qnic476wh90zg 10.31.45.182:2377

This node joined a swarm as a worker.

We can use the following command to check whether the secondary node has successfully joined the cluster:

sudo docker node ls

Sample output:

$ docker node ls
ID                            HOSTNAME   STATUS    AVAILABILITY   MANAGER STATUS   ENGINE VERSION
h673oapwzqcsoszm36dcsyx4u     worker-01     Ready     Active                          20.10.3
tg30e58pf2ebktyu5geg5hjzd     worker-02     Ready     Active                          20.10.3
vhqes84cz4ljrrj8ux9bx9jzv     worker-03     Ready     Active                          20.10.3
xj5sqdpsbs5x2pgt670dft31m *   manager       Ready     Active         Leader           20.10.3

Deploy the application on Docker Swarm

Here, we will deploy a web application on the cluster.

$ docker service create --name webserver -p 8080:80 nginx

The above command deploys the Nginx application on the cluster and exposes it on port 8080.

To confirm whether the service is running:

$ docker service ls

ID             NAME        MODE         REPLICAS   IMAGE          PORTS
z383boupqk5p   webserver   replicated   1/1        nginx:latest   *:80->80/tcp