Swarm is a native docker module to provision clustering and management of docker containers. Using docker swarm, you can communicate with different docker hosts to run and manage different containers.
In this example, swarm master and agent VMs are running on the same host OS but you configure it to run across different hosts - https://docs.docker.com/swarm/install-manual/
Docker installation guide - https://docs.docker.com/engine/installation/
I used md5 utility to generate a discovery token which will be used by swarm master and agents
TOKEN=$(md5 -q -s SOME_STRING)
docker-machine create -d virtualbox --swarm --swarm-master --swarm-discovery token://$TOKEN swarm-master
This will
- Create a new docker machine
- Configure it to be a swarm master
- Install and run swarm discovery service with swarm daemon
docker-machine create -d virtualbox --swarm --swarm-discovery token://$TOKEN swarm-agent1
docker-machine create -d virtualbox --swarm --swarm-discovery token://$TOKEN swarm-agent2
Creates two docker machines which will register with master and run as swarm agents
Run docker-machine ls to verify the docker machines for swarm master and agents are running
Run eval $(docker-machine env --swarm swarm-master) to configure your shell as swarm master
For this example, we will download the official docker image for redis and try to run it in a container
docker run -itd --name redis redis
It may take few minutes to download and run the image.
Once it returns, on running docker ps, you will notice that this image is running on one of the swarm agents (something similar as below).
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
62626fd746bd redis "docker-entrypoint.sh" 20 hours ago Up 20 hours 6379/tcp swarm-agent1/redis
Basically, swarm master instructed one of the registered agent machines (based on the scheduling strategy) to pull the image and run it in a docker container.