Docker Swarm:

Docker Swarm is native clustering for Docker, which combines a group of Docker Containing hosts to form a Cluster. In this Tutorial we will form a Three Node cluster, a Master and agent node. This will contain 3 steps.

• Set up Nodes
• Setup up a Discovery Method
• Forming Cluster

Setup Nodes for Swarm:

Upgrade Packages all system packages with

sudo apt-get update && sudo apt-get -y upgrade

Install Docker on all nodes.

curl -sSL https://get.docker.com/ | sh

Stop Docker and run it to listen on a port so swarm can connect

sudo service docker stop
sudo docker daemon -H tcp://0.0.0.0:2375 -H unix:///var/run/docker.sock

After Installing Docker engines and set it to listen on port 2375, we now have to setup a discovery backend that can form a cluster

Setting a Discovery Backend for Clustering:

Discovery backend helps in identifying and grouping the clusters. There are multiple backend discovery services available like

• Consul
• Etcd
• ZooKeeper
• libkv
• staticfile on master

In this tutorial we will use consul as Discovery Service.

docker run -d -p 8500:8500 --name=consul progrium/consul -server -bootstrap

Forming a Cluster:

On Manager Run this command 

docker run -d -p 4000:4000 swarm manage -H :4000 --replication --advertise <manager0_ip>:4000 consul://<consul_ip>:8500

run docker ps to see if swarm container is running.

On Agent Nodes run the following command to join the cluster.

docker run -d swarm join --advertise=<node_ip>:2375 consul://<consul_ip>:8500

Your cluster is now formed.

From Manager node run this commands:

docker -H :4000 run -itd ubuntu

docker -H :4000 info

You can see that ubuntu is launched in one of the agent nodes which denotes a successful Cluster.