What is Docker Swarm

Docker swarm is a container orchestration tool, meaning that it allows the user to manage multiple containers deployed across multiple host machines.

One of the key benefits associated with the operation of a docker swarm is the high level of availability offered for applications. In a docker swarm, there are typically several worker nodes and at least one manager node that is responsible for handling the worker nodes' resources efficiently and ensuring that the cluster operates efficiently

Docker Swarm has two types of services: replicated and global.

Replicated services: Swarm mode replicated services functions by you specifying a number of replica tasks for the swarm manager to assign to available nodes.

Global services: Global services function by using the swam manager to schedule one task to each available node that meets the services constraints and resource requirements.

A docker swarm is comprised of a group of physical or virtual machines operating in a cluster. When a machine joins the cluster, it becomes a node in that swarm. The docker swarm function recognizes three different types of nodes, each with a different role within the docker swarm ecosystem:

The primary function of manager nodes is to assign tasks to worker nodes in the swarm. Manager nodes also help to carry out some of the managerial tasks needed to operate the swarm. Docker recommends a maximum of seven manager nodes for a swarm.

Docker Swarm Leader Node

When a cluster is established, the Raft consensus algorithm is used to assign one of them as the "leader node". The leader node makes all of the swarm management and task orchestration decisions for the swarm. If the leader node becomes unavailable due to an outage or failure, a new leader node can be elected using the Raft consensus algorithm.

Docker Swarm Worker Node

In a docker swarm with numerous hosts, each worker node functions by receiving and executing the tasks that are allocated to it by manager nodes. By default, all manager modes are also worker nodes and are capable of executing tasks when they have the resources available to do so.

Automated Load-Balancing

Docker swarm schedules tasks using a variety of methodologies to ensure that there are enough resources available for all of the containers. Through a process that can be described as automated load balancing, the swarm manager ensures that container workloads are assigned to run on the most appropriate host for optimal efficiency.

References:

https://www.sumologic.com/glossary/docker-swarm/