What is a Docker Swarm?
Before understanding the Docker Swarm, we need to know the meaning of the term "Docker" and "Swarm."
Docker is a type of tool which is used to automate the process of application deployment as the lightweight container so that the particular application can work seamlessly in the different types of environments.
In simple words, the Docker a lightweight package of the software that has all the dependencies, libraries and frameworks that are required to run an application.
It is a kind of software platform that enables the developers to integrate the use of containers seamlessly into software applications' development process.
Another essential thing that we need to know about the Docker is that it is open-source and available for various operating systems like mac, windows, which gives developers the freedom to work on the favorite operating systems. The application also provides a control interface between the centralized machine and the host system.
The docker application's main focus is on the utilization of the containers and management of the software development process. Containers enable the software developers to package application with all necessary code and dependencies that are significantly important for that application to function in any type of computing environment.
As a result, centralized applications run seamlessly and reliably when they move from one computing environment to another. In a Docker application, a container is implemented by running an image.
So, instead of installing the "JRE" on our computer, we can download portable JRE as an image and include it in the container with our code.
What are the two types of Docker Swarm mode services?
There are two types of services provided by the Docker Swarm.
These are services performed by using the swarm manager to schedule a single task to every available Node that meets the resource requirement and service constraints.
Swarm mode replicated services performed by the user by mentioning the particular number of replica tasks for the swarm manager to assign that particular task to every available Node that has all required service constraints.
The term "swarm" refers to the group of anything e.g., nodes that form a cluster. In the Cluster, all nodes work by co-coordinating with each other, or we can say that all Nodes work as a whole.
It is basically a collection of either virtual machines or physical machines that run the Docker Application. This group of several machines is configured to make a cluster.
When the configuration of these machines gets complete and takes a form of cluster, we can still run the Docker commands that we're used to, but now they will be executed by the several machines present in the Cluster.
Here the term "Swarm" comes into play, it is the group that controls all machines available in the Cluster, and every machine that is present or joins the Cluster is considered as a Node.
Another definition of Docker Swarm
The Docker Swarm is essentially a kind of tool which allows us to create and schedule the multiple docker nodes easily. The docker swarm can also be used for a vast number of docker nodes. Each Node in the docker swarm is itself actually a docker daemon, and that demon is able to interact with the Docker API and has the benefits of being a full docker environment.
What are Docker Swarm Nodes?
A docker swarm can recognize three different types of nodes, and each type of Node plays a different role within the ecosystem of the docker swarm.
Types of Nodes
There are three types of docker swarm nodes which are given below.
Once the cluster formation process gets completed, an algorithm is known as "Raft consensus" is used to make a leader node among the Node available in the Cluster.
The leader node takes care of tasks such as task orchestration decisions for the swarm, managing swarm. If the leader node gets down or becomes unavailable due to any reason, the leadership is transferred to another Node using the same algorithm.
Once the Cluster gets established successfully, an algorithm is used to choose one of them as the leader node, and that algorithm is known as the "Raft consensus".
The Node which is chosen as the leader has the responsibility to make all of the swarm management, also make the decisions for the swarm.
If somehow the leader node becomes unavailable due to some fatal error or hardware failure, another node is against chosen from the available nodes.
Inside the docker swarm that contains a vast number of hosts, every worker node performs the received tasks/operations. Also, it executes each task allocated by the leader node(or manager node).
In general, all Nodes are the worker nodes even the manager node is also a worker node and capable of performing the task/operations when required resources are available for them.
What is Docker Swarm used for?
The Docker swarm is one of the container orchestration tools that allow us to manage several containers that are deployed across several machines.
One of the significant advantages of swarm's operations is the significant level of availability for the Applications.
A docker swarm usually contains specific numbers of nodes and also has one manager node at least.
The manager node operates or controls every node present in the Docker swarm. It is also responsible for handling all available nodes and ensuring that all of them work efficiently or the Cluster works efficiently and seamlessly.