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What is a Docker Swarm? - Complete Guide

What is a Docker Swarm? - Complete Guide

In this comprehensive guide, from what Docker Swarm is to all its fundamentals, we’ll cover everything you need to know about Docker Swarm. 

Table of Contents

Here is a video explanation of the fundamentals of Docker:

What is Docker Swarm?

Docker Swarm is a container orchestration solution that allows users to manage a cluster of Docker nodes and deploy containerized applications at scale. It operates by abstracting the underlying technology and providing users with a single virtual system. This enables customers to administer their containerized apps as if they were operating on a single system, even if they are spread over numerous hosts.

Docker Swarm is a container orchestration solution that simplifies the management of multiple Docker nodes and the deployment of containerized applications on a larger scale. It achieves this by creating a virtual system, allowing users to handle their containerized apps as if they were running on a single system, even when spread across different hosts.

Container orchestration is like being the conductor of an orchestra for your containerized applications. It’s the organized way of making sure all the containers (like small, independent software packages) work together harmoniously. Docker Swarm acts as the conductor, ensuring that your containers on different machines play their parts seamlessly, making your applications run smoothly, no matter how complex they are.

Docker Swarm works by combining numerous Docker hosts into a single virtual system known as a swarm. The swarm is made up of numerous nodes, with one functioning as the manager and the others as workers.

The management node is in charge of managing container deployment across the worker nodes, while the worker nodes are in charge of operating the containers.

Docker Swarm Architecture

The Docker swarm setup has two kinds of nodes: management nodes and worker nodes. The manager nodes oversee the swarm, handle job schedules, and manage the swarm’s status. On the other hand, worker nodes take on tasks given to them by the manager nodes.

When a swarm is formed, one of the nodes is identified as the first management node. This node is in charge of forming and controlling the swarm. Additional management nodes can be added for high availability and redundancy.

Each swarm node has a Docker engine that allows it to execute containers. The management nodes also run the swarm mode routing mesh, which allows containers to interact even if they are on distant nodes.

When a container joins the swarm, it has a job to do. This job is called a task, and it represents one container doing a specific piece of work. The management node decides which worker node should handle the task, and then that worker node runs the container as a task instance.

The routing mesh in the Docker swarm architecture has a significant role to play. When a container is added to the swarm, it receives a virtual IP address (VIP) to connect with other containers in the swarm. The routing mesh ensures that network traffic is directed correctly to the respective container, even if it is located on a different node.

Docker swarm also supports the use of services, which are groups of tasks that are deployed together. Services can be configured with a desired number of replicas, and the manager node will ensure that the correct number of tasks are running at all times. This makes it easy to scale services up or down as demand changes.

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Have a look at the Docker Tutorial to understand the fundamentals of Docker.

Features of Docker Swarm

“Docker is a tool designed to make it easier to create, deploy, and run applications by using containers.”

This quote by Docker’s founder, Solomon Hykes, captures the fundamental essence of Docker as a technology that uses containers to simplify application development, deployment, and maintenance.

Containers are lightweight, portable, and self-contained environments that encapsulate a program and its dependencies, allowing for consistent and reliable deployment across several settings. Docker makes it simple to construct, package, and distribute these containers, allowing developers to focus on creating code rather than worrying about infrastructure.

Features of Docker Swarm

Docker Swarm has several significant features, including:

High Availability: Docker Swarm enables high availability by automatically monitoring the health of containers running on worker nodes. When a container fails, it immediately replaces it with a new one, ensuring that applications stay available and responsive even when hardware or software fails.

Load Balancing: It includes load balancing features that enable customers to easily spread traffic across several instances of a service. Even if the container is executing on a different node, the Swarm mode routing mesh guarantees that traffic is directed to it.

Scaling: It makes it simple to scale apps up or down as demand changes. Services may be set up with the required number of replicas, and the management node will guarantee that the proper number of jobs are executed at all times. This makes it simple to handle traffic surges or scale down as demand falls.

Rolling Updates: Docker Swarm offers rolling updates, allowing customers to upgrade their apps without incurring downtime. When a new version of an application is released, Docker Swarm will generate new containers running the updated version and gradually replace the old ones with the new ones, ensuring that the application stays available during the update process.

Multi-host Networking: It has multi-host networking capability, allowing containers to connect with one another even if they are executing on different nodes. This simplifies the deployment of distributed applications that span several servers.

Compatibility with Docker Compose: It is compatible with Docker Compose, enabling users to utilize Compose files to create their services and subsequently deploy them to a swarm. This simplifies the deployment process for complex applications that consist of multiple services and dependencies.

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Docker Swarm Vs. Kubernetes

Here’s a comparison of Docker Swarm and Kubernetes, two prominent container orchestration platforms:

FeaturesDocker SwarmKubernetes
ScalabilityIdeal for small to medium-sized deployments.Suitable for large-scale deployments.
NetworkingMulti-host networking is simple and easy to set up.More complicated networking with numerous plugins available.
SecurityMutual TLS authentication, encryption, and role-based access control are supported.Supports network policies, security contexts, and secrets, among other security features.
ExtensibilityExtensibility is limited due to a smaller ecosystem of third-party tools and plugins.A large ecosystem of third-party tools and plugins, such as operators, Helm charts, and CRDs, is available.
CommunitySmaller community with fewer resources and possibilities for assistance.A large and active community with a wealth of information and support choices.
Load balancingLoad balancing is built-in with a Swarm mode routing mesh.
Built-in load balancing with Kube-proxy.
High availabilityAutomatic container failover and rescheduling are supported.Automatic pod failover and rescheduling are supported.
Ease of useSimple architecture and fewer ideas to understand make it simple to learn and utilize.With a broader architecture and more ideas to understand, it is more difficult to learn and utilize.

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Docker Swarm Vs. Docker Compose

Here’s a comparison of Docker Swarm and Docker Compose, two tools for managing Docker containers:

Features Docker SwarmDocker Compose
DeploymentContainers are deployed across numerous nodes in a swarm cluster.Containers are deployed on a single node.
OrchestrationSwarm cluster orchestration for several Docker hosts.Docker orchestration for a single host.
Ease of useSimple to understand and utilize, having a simple architecture.Simple to understand and utilize, having a simple architecture
Use CaseSuitable for large-scale deployment and management of containerized applications.It is appropriate for designing and testing containerized applications.
ScalingSupports horizontal service scalability throughout the cluster.Does not allow for horizontal scaling.
NetworkingThe overlay network driver enables multi-host networking.Single-host networking with user-defined networks is supported.
Rolling updatesRolling updates are supported with no downtime.Rolling updates are supported with no downtime.
ConfigurationFor configuration, YAML files are used.For configuration, YAML files are used.

Intellipaat provides you with the Top 35+ Docker Interview Questions to help you practice and ace your interviews.

Setting up Docker Swarm Cluster

Let’s set up a Docker Swarm manager node and a service on Ubuntu 16.04 using Docker commands. To begin, ensure the latest Docker Engine is installed on the host. Let’s begin with these steps:

1. Check the Docker Version and Download the Container:

First, confirm the Docker version on the host. Then, download a container, for example, MySQL, with the command:

docker pull mysql

This command fetches the latest MySQL container.

After downloading, run the container using:

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

Confirm the container is running with:

docker ps -a

2. Create Docker Swarm:

Initialize a Swarm cluster by specifying the manager node’s IP address:

docker swarm init --advertise-addr

Note: You can create a worker node by copying the “swarm init” command output and executing it on another host. Ensure both hosts have the latest Docker Engine installed.

Check the nodes with:

docker node ls

3. Launch Service in Swarm Mode:

Deploy a service on the manager node, for instance, a simple ‘HelloWorld’ service:

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

Confirm the service with:

docker service ls

This completes the setup of your Swarm cluster on Ubuntu 16.04.

Docker Swarm Commands

The following table shows some of the Docker Swarm CLI commands with their usages and why they are used.

CommandDescriptionCommand Usage
swarm initInitiates a swarm, designating the executing docker engine as a manager node.docker swarm init [OPTIONS]
swarm joinJoins the swarm cluster as a node, with the option to join as a manager or worker based on the token.docker swarm join [OPTIONS] HOST:PORT
service createCreates a new service.docker service create [OPTIONS] IMAGE [COMMAND] [ARG…]
service lsLists the available services.docker service ls [OPTIONS]
service inspectDisplays detailed JSON information about a specified service.docker service inspect [OPTIONS] SERVICE [SERVICE…]
service scaleScales up or down services to the desired number, applicable only to replicated services.docker service scale SERVICE=REPLICAS [SERVICE=REPLICAS…]
service rmRemoves one or more services from the swarm.docker service rm SERVICE [SERVICE…]
service updateUpdates the specified service.docker service update [OPTIONS] SERVICE
service psLists running tasks for specified services.docker service ps [OPTIONS] SERVICE [SERVICE…]


Docker is a popular and effective platform for containerizing programs, allowing developers to build, package, and distribute their code consistently and dependably. Docker facilitates application development and deployment by using lightweight and portable containers, making it simpler to execute apps across several environments, from development to production. It also has sophisticated features like scalability, load balancing, and high availability, making it appropriate for large-scale deployments. 

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