What is Docker Swarm: Modes, Example and Working [Updated] (2024)

What is Docker and Docker Container?

Docker is a tool used to automate the deployment of an application as a lightweight container so that the application can work efficiently in different environments.

Docker container is a lightweight software package that consists of the dependencies (code, frameworks, libraries, etc.) required to run an application.

We can use Docker Swarm to make Docker work across multiple nodes, allowing them to share containers with each other. It's an environment where you can have various Docker images running on the same host operating system.

Now, that we have understood what Docker and Docker containers are, let us next look into what Docker swarm is.

What is Docker Swarm?

Docker Swarm is an orchestration management tool that runs on Docker applications. It helps end-users in creating and deploying a cluster of Docker nodes.

Each node of a Docker Swarm is a Docker daemon, and all Docker daemons interact using the Docker API. Each container within the Swarm can be deployed and accessed by nodes of the same cluster.

There are five critical elements within a doctor environment:

1. Docker container
2. Docker daemon
3. Docker images
4. Docker client
5. Docker registry

Consider an environment having Docker containers as shown:

If one of the containers fails, we can use the Swarm to correct that failure.

Docker Swarm can reschedule containers on node failures. Swarm node has a backup folder which we can use to restore the data onto a new Swarm.

Features of Docker Swarm

Some of the most essential features of Docker Swarm are:

• Decentralized access: Swarm makes it very easy for teams to access and manage the environment
• High security: Any communication between the manager and client nodes within the Swarm is highly secure
• Autoload balancing: There is autoload balancing within your environment, and you can script that into how you write out and structure the Swarm environment
• High scalability: Load balancing converts the Swarm environment into a highly scalable infrastructure
• Roll-back a task: Swarm allows you to roll back environments to previous safe environments

Let us extend our learning on what is Docker swarm, let us look into the swarm mode key concepts

Swarm Mode Key Concepts

Service and Tasks

• Docker containers are launched using services.
• Services can be deployed in two different ways - global and replicated.

Global And Replicated Service

• Global services are responsible for monitoring containers that want to run on a Swarm node. In contrast, replicated services specify the number of identical tasks that a developer requires on the host machine.
• Services enable developers to scale their applications.
• Before deploying a service in Swarm, the developer should implement at least a single node.
• Services can be used and accessed by any node of the same cluster.
• A service is a description of a task, whereas a task performs the work.
• Docker helps a developer in creating services, which can start tasks. However, when a task is assigned to a node, the same task cannot be attributed to another node.

Node

• A Swarm node is an instance of the Docker engine.
• It is possible to run multiple nodes on a single server. But in production deployments, nodes are distributed across various devices.

Do you have any questions in this article “what is Docker swarm”. If yes, please leave your comments below.

Kubernetes vs. Docker Swarm

The table below illustrates the differences between Kubernetes vs. Docker Swarm:

To strengthen our understanding of what Docker swarm is, let us look into the demo on the docker swarm.

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Demo On Docker Swarm For Beginners

This tutorial “What is Docker Swarm” requires two hosts, which can either be Virtual Machine or AWS EC2.

The demo shows how to build and deploy a Docker Engine, run Docker commands, and install Docker Swarm.

Prerequisites:

• Ubuntu 64-bit operating system
• An ubuntu account with Sudo privileges
• Command-line terminal
• Docker software repositories (optional)

Step 1: Update Software Repositories

Run the following command on the terminal:

sudo apt-get update

Step 2: Uninstall Old Versions of Docker

Before proceeding, uninstall the old Docker software and use the following command:

sudo apt-get remove docker docker-engine docker.io

Step 3: Install Docker

To install Docker on Ubuntu, run the following command:

sudo apt install docker.io

Step 4: Set-up Docker

Set-up and run Docker service by entering the following commands in the terminal window:

sudo systemctl start docker

sudo systemctl enable docker

Step 5: Verify Docker Version

To check the installed Docker version, enter the following command:

sudo docker --version

Step 6: Run Docker Container

To run a Docker container, it’s important to pull a Docker Image (such as MySQL) from Docker Hub.

sudo docker pull mysql

sudo docker run -d -p0.0.0.0:80:80 mysql:latest

Now, Docker pulls the latest MySQL image from the hub.

List down all the available Docker images on your machine by using the following command:

sudo docker ps -a

Step 7: Create Swarm

Here, create a cluster with the IP address of the manager node.

sudo Docker Swarm init --advertise-addr 192.168.2.151

Subsequently, you should see the following output:

Manager Node

This means that the manager node is successfully configured.

Now, add worker node by copying the command of the “swarm init” and paste the output onto the worker node:

sudo Docker Swarm join --token SWMTKN-1- xxxxx

Your worker node is also created if you see the following output:

Worker Node

Now, go back to the manager node and execute the following command to list the worker node:

sudo docker node ls

Here, you must see the worker node in the following output:

Swarm Cluster - Docker Swarm

The above image shows you have created the Swarm Cluster successfully. Now, launch the service in Swarm Mode.

Go to your the manager node and execute the command below to deploy a service:

sudo docker service create --name HelloWorld alpine ping docker.com

By executing the above command, you can access the HelloWorld file from the remote system.

To see the output, you can check the services with the following command:

sudo docker service ls

Finally, you should be able to see the following output:

Service Created - Docker Swarm

And that’s it! Well done, you have successfully installed and configured the Swarm cluster on Ubuntu 16.04. Also, whenever required, you can effortlessly scale your application with no performance issues.

Conclusion

In this write-up, we learned what is Docker Swarm, along with that understood the Swarm mode key concepts and how Docker Swarm works. We also explored Kubernetes vs. Docker Swarm, and why we use Docker Swarm. In the end, we also saw a case study on ‘How to set up Swarm in the Docker ecosystem’. Do you have any questions so far? Please feel free to put it in the comments section of this article “what is Docker swarm”, our experts will get back to you at the earliest.

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