Additional menu

Code Leaks

Your go-to place for programming guides

WHAT-IS-DOCKER-SWARM-AND-HOW-TO-CREATE-ONE
You are here: Home / Linux / What is Docker Swarm and How to create one

What is Docker Swarm and How to create one

Last Updated On By

In this article, we will see what is Docker swarm and how to create a one? With manager and worker nodes. Different operations have been applied to the containers created. After containers, we will see how to create services for those containers and assign them that.

What is container orchestration?

Having multiple containers on for different things like hosting or deployment with thousands of other Linux distribution can be hectic to manage. It would be very time consuming to manage all the containers manually, for that you would most likely go towards an automated solution. Container orchestration manages, deploys, scales, and networks the containers without any explicit interference from the host.
docker sawrm
The container’s lifecycle is also managed in a dynamic environment so the resources can be accessed on virtual or physical node’s operating system. The deployment, scaling, resource allocation, load balancing, and health monitoring are all the responsibilities that come under the umbrella of container orchestration.

What is Docker Swarm ?

Docker swarm is a tool for container orchestration that allows the user to manage and monitor containers. You can analyze those that have been deployed on multiple host machines.

Also, you can manage clusters of containers easily and can treat them as a single virtual machine.

There are few roles in the Docker swarm that needs your attention.

Manager Node: the manager node is responsible for managing all the nodes connected in the swarm. It assigns services and keeps track of the task assigned to each container. Moreover, the manager node is also responsible to assign the resources each container would require to complete their task. It’s the manager node that creates the worker node once initialized in the swarm, then allocates IPs to the created worker nodes. Services: defines the tasks that need to be executed by the worker nodes. These services are the core part of the functionality and define what each designated node needs to be doing. Tasks: one service can have multiple tasks and these tasks are defined by which commands to be executed for the services to serve its operations. These tasks informs the containers to execute the listed commands to complete a service. Workers: the worker nodes come under the supervision of the manager node. After the assigned task, they make sure the execution is done and keeps monitoring them.

Building a docker swarm

The first thing you need to do is initialize a swarm with a manager node. You can do this by running the following command.
docker swarm init --advertise-addr  <manger IP>
add manager node
Let’s break this command and understand what is happening. The docker swarm init initializes the swarm and the flag –advertise-addr, advertises the IP address assigned to the manager node. 1. Adding a worker to a swarm This command will enable you to add workers in the swarm by adding them with the token id you have been provided.
docker swarm join --token <token id>

As I have already made a worker node from this token it is giving me the error of node already existed in the swarm, but if you run it as a new worker node it will give the message “This node joined a swarm as a worker. “

1. Docker info

If you wanted to summarize information on how many worker nodes are there in your swarm or what are the node ids and other info you can run the following command.

docker info
docker info
1. Number of nodes You can identify the number of nodes in the swarm by running the ls command for connected nodes.
docker node ls
number of nodes
1. Remove node from swarm You can make the node leave the swarm by executing any of the two following commands. 
docker node rm <node-id>
docker node rm –f <node-id>
-f flag means to forcefully remove the node from the swarm as few don’t allow direct removal.
remove docker node
Docker swarm service As we have made nodes of either manager or workers as a part of the swarm, we need to add the services each node will be designated to. The service is used to deploy the application image; it can be an image of ngnix, WordPress, or others.
docker swarm service

     1.    Creating a service 

docker service create –replicas <number-of-replicas> --publish <port-mapping> <image>
creating service
All the three service replicas have been installed with Ngnix as their image. You can type the following command to find the docker services listed. 1. Service information
docker service ls

   

docker service inspect --pretty <service-id>
1. Removing a service You can remove the created service by the following command.
docker service rm <service >
remove docker service
Now check through the ls command if the service has been removed or not.

Conclusion

Docker swarm is an excellent resource to be able to manage multiple containers and collectively apply operations. This saves up time and effort to look at different containers running on either virtual or physical machines.