<\/path>\n\t\t\t<\/svg>\n\t\t<\/button><\/figure><\/div>Next, check that the Docker service is up and running:<\/p>
sudo systemctl status docker<\/pre>You should see a status like active (running)<\/strong>, confirming that the Docker daemon is working properly.<\/p>\n
\n\t\t\t\n\t\t\t\t<\/path>\n\t\t\t<\/svg>\n\t\t<\/button><\/figure><\/div>To exit the status output, press Ctrl + C<\/strong>.<\/p>2. Initialize the swarm manager<\/strong><\/h3>Run on<\/strong>: manager node.<\/p>After installing Docker on all nodes, switch your focus to the manager<\/strong> node – this is where you’ll create the Docker swarm. First, make sure you know the manager node’s IP address.<\/p>For Hostinger VPS customers, you can find the IP address in the VPS details<\/strong> section on the Overview<\/strong> page – the same place where you changed the hostname earlier.<\/p>Once you have the IP address, run the following command to initialize the swarm. Replace [manager node’s IP]<\/strong> with your actual VPS IP:<\/p>docker swarm init --advertise-addr [manager node's IP]<\/pre>This command generates an output similar to:<\/p>
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\n\t\t\t\n\t\t\t\t<\/path>\n\t\t\t<\/svg>\n\t\t<\/button><\/figure><\/div>Copy and save the join command – you’ll need it to connect the worker nodes to the swarm.<\/p>
To confirm that the swarm started successfully, run:<\/p>
docker info<\/pre>This shows information about the swarm state.<\/p>
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\n\t\t\t\n\t\t\t\t<\/path>\n\t\t\t<\/svg>\n\t\t<\/button><\/figure><\/div>Then, check the list of nodes in the swarm:<\/p>
docker node ls<\/pre>You should see details like node ID, hostname, status, availability, and role.<\/p>
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\n\t\t\t\n\t\t\t\t<\/path>\n\t\t\t<\/svg>\n\t\t<\/button><\/figure><\/div>\n\n
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Pro tip<\/h4>\n If you want to add nodes but forgot the token, run this command on the manager<\/strong> node to display it again:docker swarm join-token worker<\/strong><\/p>\n <\/div>\n\n\n\n<\/p>3. Add worker nodes<\/strong><\/h3>Run on<\/strong>: worker1 and worker2 nodes.<\/p>Now, move on to the worker1<\/strong> node and run the join command you copied from the manager:<\/p>docker swarm join --token [join token] [manager node's IP]:2377<\/pre>If you see the message “This node joined a swarm as a worker<\/strong>,” the node has joined the swarm successfully.<\/p>\n
\n\t\t\t\n\t\t\t\t<\/path>\n\t\t\t<\/svg>\n\t\t<\/button><\/figure><\/div>Repeat the same process on worker2<\/strong> or any additional nodes to connect them to the swarm.<\/p>\n\n\n
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Pro tip<\/h4>\n Each time you add a new node, go back to the manager<\/strong> node and run docker node ls<\/strong> to confirm that the new node has indeed joined the swarm.<\/p>\n <\/div>\n\n\n\n<\/p>4. Deploy your first service<\/strong><\/h3>Run on<\/strong>: manager node.<\/p>Return to the manager<\/strong> node to deploy a test service named hello-world<\/strong>. Although this is just a test service and you’ll delete it in the next step, practicing this will help you become familiar with service management in Docker Swarm.<\/p>Here’s the command to create the hello-world<\/strong> service:<\/p>docker service create --replicas 1 --name hello-world alpine ping docker.com<\/pre> \ndocker service create<\/strong> – starts the service creation in Docker Swarm.<\/li>\n\n\n\n–replicas 1<\/strong> – defines the number of service replicas to run. In this case, it’s just 1<\/strong>.<\/li>\n\n\n\n–name hello-world<\/strong> – sets the service name as hello-world<\/strong>.<\/li>\n\n\n\nalpine ping docker.com<\/strong> – uses the alpine<\/strong> image to ping docker.com<\/strong> as a simple test.<\/li>\n<\/ul>\n
\n\t\t\t\n\t\t\t\t<\/path>\n\t\t\t<\/svg>\n\t\t<\/button><\/figure><\/div>After that, use the following command to list the services running in the swarm:<\/p>
docker service ls<\/pre>\n
\n\t\t\t\n\t\t\t\t<\/path>\n\t\t\t<\/svg>\n\t\t<\/button><\/figure><\/div>5. Inspect and scale services<\/strong><\/h3>Run on<\/strong>: manager node.<\/p>After deploying your test service, it’s time to inspect and scale it within the swarm.<\/p>
Inspect the service details<\/strong><\/p>Check your hello-world<\/strong> service details with the command below:<\/p>docker service inspect --pretty hello-world<\/pre>This will provide detailed information about the service, including its ID, replicas, and other settings. The –pretty<\/strong> flag formats the output to make it more readable.<\/p>\n
\n\t\t\t\n\t\t\t\t<\/path>\n\t\t\t<\/svg>\n\t\t<\/button><\/figure><\/div>See where the service is running<\/strong><\/p>Next, verify which nodes are running the service by executing:<\/p>
docker service ps hello-world<\/pre>This will list all tasks associated with the hello-world<\/strong> service and the nodes on which they are running.<\/p>\n
\n\t\t\t\n\t\t\t\t<\/path>\n\t\t\t<\/svg>\n\t\t<\/button><\/figure><\/div>Scale the service<\/strong><\/p>To scale the service, change the number of replicas. For example, to scale hello-world<\/strong> to three replicas, run:<\/p>docker service scale hello-world=3<\/pre>Docker Swarm will then create additional replicas of the service on available nodes.<\/p>
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\n\t\t\t\n\t\t\t\t<\/path>\n\t\t\t<\/svg>\n\t\t<\/button><\/figure><\/div>Review the updated tasks<\/strong><\/p>After scaling, check how the tasks are distributed across the nodes:<\/p>
docker service ps hello-world<\/pre>You should see that the tasks are now evenly distributed across three nodes, compared to the previous state when you ran the same command.<\/p>
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\n\t\t\t\n\t\t\t\t<\/path>\n\t\t\t<\/svg>\n\t\t<\/button><\/figure><\/div>Remove the service<\/strong><\/p>Once you’ve finished inspecting and scaling the service, remove it from the swarm by running:<\/p>
docker service rm hello-world<\/pre>This command safely deletes hello-world<\/strong> from the swarm.<\/p>\n
\n\t\t\t\n\t\t\t\t<\/path>\n\t\t\t<\/svg>\n\t\t<\/button><\/figure><\/div>Confirm the service removal<\/strong><\/p>Verify that the service has been removed from the swarm with this command:<\/p>
docker service ls<\/pre>If the hello-world<\/strong> service was successfully removed, it will no longer appear in the list.<\/p>6. Apply rolling updates to services<\/strong><\/h3>Run on<\/strong>: manager node.<\/p>A rolling update lets you update services without downtime. Docker Swarm updates one replica at a time and moves to the next replica once the update is complete.<\/p>
You’ll first deploy a service using the Redis 7.4.0<\/strong> container tag. Then, upgrade the service to 7.4.1 <\/strong>with the rolling update approach.<\/p>Deploy a Redis service<\/strong><\/p>Start by deploying a service using an older version of the Redis Docker image so you can update it later:<\/p>
docker service create --name redis --replicas 3 redis:7.4.0<\/pre>\n
\n\t\t\t\n\t\t\t\t<\/path>\n\t\t\t<\/svg>\n\t\t<\/button><\/figure><\/div>Update the service<\/strong><\/p>To update the service, run the following command, specifying a newer version of the Redis image:<\/p>
docker service update --image redis:7.4.1 redis<\/pre>Docker Swarm will gradually replace the old containers with the updated ones, ensuring zero downtime.<\/p>
Inspect the service for the updated version<\/strong><\/p>To check the updated service version and confirm the new image, execute:<\/p>
docker service inspect --pretty redis<\/pre>\n
\n\t\t\t\n\t\t\t\t<\/path>\n\t\t\t<\/svg>\n\t\t<\/button><\/figure><\/div>Check which nodes are running the service<\/strong><\/p>To monitor the rolling update and see which containers are still running and which ones are being replaced, use:<\/p>
docker service ps redis<\/pre>You’ll see a list of containers with the desired state showing running<\/strong> for the updated containers and shutdown<\/strong> for the old ones.<\/p>\n
\n\t\t\t\n\t\t\t\t<\/path>\n\t\t\t<\/svg>\n\t\t<\/button><\/figure><\/div>7. Lock your swarm<\/strong><\/h3>Run on<\/strong>: manager node.<\/p>When you lock your swarm, it requires an encryption key to unlock and change its configuration. This ensures that only authorized users can access and modify the swarm, preventing unauthorized users from altering the cluster.<\/p>
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Important!<\/strong> You don’t need to unlock the swarm if you just want to join a new node to it.<\/p><\/div>\n\n\n\n<\/p>
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