Why is Docker Swarm the Right Choice for your Next Project?

Those days are gone when developers used to rely on virtual machines for deploying multiple isolated services across different environments. Owing to increased agility and higher portability, Docker has replaced VMs by making deployment easy and efficient.

Businesses are moving their workloads over to containerization technology owing to the ease of running applications without the need to launch an entire virtual machine.

According to a global survey by Statista (in 2021), 96% of respondents worldwide stated that they were using containerization technology as they find working with containers convenient and comfortable.

Container technology is gaining popularity in cloud-native development as well as multi-cloud environments. Why? The below infographic from a global survey by Statista represents why developers are big fans of container technology.

The Primary Benefits of Container technology

Source

Talking of container technology, Docker accounted for 27% of the Containerization technology Market share as of 2022, leaving LXC and Kubernetes behind at 2^nd and 3^rd places respectively.

Why Choose Docker Swarm?

Developers are vouching for Docker Swarm due to its ease of container orchestration management and automated load-balancing feature. Along with offering high scalability and security, it is the best and most reliable tool to use for your next project. Why?

This blog explains it all. It is a comprehensive guide to Docker Swarm. By the end, you will have a better understanding of Docker swarm, its key concepts, its service nodes, advanced features, key benefits, and steps of implementation. We have also added some interesting comparisons of the docker swarm with the latest container technologies.

But before we start with docker swarm, we must understand important aspects of Docker and how its implementation is different from virtual machines. 

What is Docker?

Docker is an open-source PaaS (Platform as a Service) based OS-level virtualization tool used by developers to automate the deployment of a software application in lightweight packages called containers. It acts as a central interface between the centralized machine and the host system.

Docker Container: Docker container refers to a lightweight software package packed with isolated dependencies (code, libraries, framework, etc) that are necessary to render an application smoothly and reliably across multiple computing environments.

Docker Engine: Docker engine is software that hosts the containers.

The below infographics represent how Dockers are different from Virtual Machines.

What is Docker Swarm?

Docker swarm is a container orchestration tool that helps developers create, deploy, and manage a cluster of docker nodes in a docker application.

Each node in a docker swarm is a docker daemon. These docker daemons are instances that connect Docker Engine to swarm. They coordinate with each other using docker API. Containers in a docker swarm can be deployed or accessed by the nodes of the same cluster.

A docker environment consists of five critical elements that are docker container, docker nodes, docker images, docker client, and docker registry. Each of the elements is elaborated below:

Docker Container

Docker containers are the active operational instances of Docker images. Docker images are read-only files whereas the containers will contain executable and transient content. The users can interact with them while the administrators can access Docker commands for redefining the parameters.

Docker Nodes

When the Docker engine participates in the swarm, it turns into Docker node. With Docker run, you can run one or more nodes on a single physical computer or cloud server. Generally production swarm deployments comprise Docker nodes.

Docker Images

Building blocks for containers are called Docker images. Docker images are like snapshots for virtual machines. They are immutable and read-only files including the source code. They mainly contain libraries, dependencies, tools, and additional files to run an application.

Docker Client

The most crucial way adapted by Docker users is to interact with Docker which is called Docker Swarm. Using commands such as docker run enables clients to send them to docker which will carry them out. 

Docker Registry

Docker registry is a stateless yet highly scalable server-side application that can store and as well help you distribute Docker images. The registry source code can be found on Git.

An environment with a docker container is represented below:

In case one container fails, the docker swarm corrects the failure.

What is a Swarm Cluster? Which are the types of Swarm Nodes?

Swarm means the formation of a group or a cluster of nodes working together in a docker environment.

There are three types of nodes in a docker swarm:

Leader Node:

Once the cluster is formed, a leader node is rendered by using the ‘Raft Consensus’ algorithm. It takes all the decisions related to task orchestration and management.

In any case, if the leader node becomes unavailable, its responsibility is transformed to another node by rendering the same algorithm.

Manager Node:

A manager node allocates the task to worker nodes and makes sure that tasks are executed well.

Worker Node:

A worker node checks for an assigned task and executes it. You need a manager node to create a worker node.

How does Docker Swarm Work?

The containers are launched using services. A service refers to a collection of tasks that are to be executed by worker nodes. It is created by using Command-Line Interface (CLI).

A manager node allocates, schedules, and dispatches tasks to worker nodes as well as orchestrates overall task management.

It consists of an API that establishes communication between manager nodes and worker nodes using the HTTP protocol.

The manager node keeps a track of the worker nodes and tries to maintain the desired state of a cluster.

What are Docker Swarm Modes?

By now you are aware that docker containers are launched using services. There are two docker swarm modes to deploy these services:

Global Service Mode:

In the global mode, a manager node schedules a single task to all the available worker nodes that fulfill resource requirements and service constraints. Global services monitor the containers that want to run on swarm mode.

Replicated Service Mode:

Here users define a specific number of replica tasks for manager nodes to allocate. Manager nodes are commanded to allocate these tasks to specific worker nodes that meet the requirements and service constraints. Replicated services decide the number of replicated tasks that a developer requires to implement on the host machine. 

What are the Key features of Docker Swarm?

Some key features offered by docker swarm are:

Decentralized Access:

With docker swarm, developers can easily access and manage multiple computing environments.

Cluster Management:

Developers can create a swarm using the docker engine. Developers do not require additional orchestration software.

Multi-host Networking:

Swarm contains multiple overlay networks. While deploying a service, developers need to specify the network for deployment. The swarm manager automatically assigns the desired network address to the container while initializing or updating the application.

Auto Load Balancing:

When a service is deployed on a particular port, the swarm automatically balances the load of that port.

High Scaling:

While scaling up or down, the swarm manager automatically adapts to the desired state by adding or removing tasks from the cluster.

Easy Roll-back:

Swarm enables rolling back from new environments to previously used safe environments.

Intact Security:

Swarm hosts secure communication between manager nodes and client nodes.

Advantages of Docker swarm

Simplified Cluster Management: 

Docker Swarm simplifies the process of managing and scaling a cluster of Docker containers by providing an easy-to-use interface.

Improved Resource Utilization:

Docker Swarm allows multiple containers to run on a single host, resulting in efficient use of resources.

High Availability: 

Docker Swarm provides high availability by allowing containers to be deployed across multiple nodes.

Automatic Load Balancing: 

Docker Swarm automatically distributes traffic among containers to ensure optimal performance.

Multi-Cloud Support: 

Docker Swarm allows containers to be deployed across multiple cloud providers, allowing for greater flexibility and scalability.

Cost Reduction: 

Docker Swarm offers cost savings by allowing multiple containers to be deployed on a single host, reducing the number of physical servers needed.

The Design Advantage of Containers:

With docker swarm, developers can enjoy the advantage of containers. As compared to handling complex virtual machines, containerization allows efficient and comfortable cloud computing.

Increased Application Availability:

Docker swarm offers increased application availability through redundancy. Developers can easily implement multiple manager nodes to ensure the functioning of a system at full throttle. In case one manager node fails, it can quickly be rolled back and replaced. Swarm allows a maximum of seven manager nodes at a time.

Optimum Efficiency:

Swarm orchestrates tasks and ensures that enough resources are available for containers. Owing to its automated load-balancing functionality, swarm ensures efficient workload distribution across all containers. Resulting in optimal efficiency.

Health Monitoring:

With a swarm, monitoring takes place at a micro level. The manager nodes continuously monitor worker nodes and swiftly replace nodes on failure. This ensures the proper formation and working of a cluster in the desired state. Hence applications can render smoothly in all computing environments.

With docker swarm, developers can enjoy the advantage of containers. As compared to handling complex virtual machines, containerization allows efficient and comfortable cloud computing.

How to Implement a Docker Swarm Mode?

You can get started with Docker swarm in a few steps

1. Initialize a cluster of docker engines in the swarm mode.

You can use this command to initialize a swarm

docker swarm init [OPTIONS]

2. Add nodes to swarm

Use this command to add a node to the docker swarm.

docker swarm join [OPTIONS] HOST:PORT

Note: The created node will join as a manager node or a worker node based on the token you pass with the token-flag.

3. Deploy service to swarm.

You can use this command to create a docker service. This is a cluster management command, so it must be executed on swarm manager nodes.

docker service creates [OPTIONS] IMAGE [COMMAND] [ARG…]

4. Inspect docker services

You can use this command to inspect a particular service. All details of that service will be displayed in JSON format

docker service inspect [OPTIONS] SERVICE [SERVICE…]

5. Manage the docker services

You can use this command to review the complete list of all services in a particular network.

docker service ls [OPTIONS]

You can use this command to remove a particular service from the network.

docker service rm SERVICE [SERVICE…]

Kubernetes v/s Docker Swarm

Kubernetes	Docker Swarm
Installation is complex	Simple installation
Better choice for large-scale production deployments	Better choice for small-scale deployments
Manual load balancing	Automated load balancing
Lower scalability	Highly scalable
Slower deployment	Deployment is quick and easy
Difficult to set up a cluster	Easy to set up a cluster
While switching platforms, it is mandatory to re-write the YAML command	Containers can be easily deployed on multiple platforms
Requires tools (in-built) to manage the processes	No tools are required for logging or monitoring
Offers high availability when pods are distributed among nodes	Increased application availability achieved through redundancy
Can be shared with containers having similar pods	It can be shared with any container.

Docker Swarm v/s Docker Compose:

Docker Swarm	Docker Compose
Multiple containers are created on multiple hosts	Multiple containers are created on a single host
No file is required. You can manage different hosts on a cluster.	YAML is used to manage different containers as a single service
Highly scalable	The container runs on a single host. Scaling is not required
Has fault tolerance. Swarm quickly corrects failed containers and reschedules dispatch	Has no tolerance for faults and failures
It can be installed with the in-built CLI.	It is a standalone binary and needs to be installed separately

Wrapping up

With this, the blog covers every aspect of docker swarm. However, it is always better said than done. From the emergence of container technology to the implementation of docker swarm technology, a detailed guide is provided for your reference. Theoretically, it may seem easy unless practically implemented. A reliable tech expert can always help you to make the right choice while making informed decisions.