Docker Swarm

Sample 3 node Vagrant setup for getting started with Docker swarm

watch whole demo here

Installation

Install Vagrant Binary from here
Download ubuntu/trusty64 box from vagrant using the command vagrant box add ubuntu/trusty64
Clone this repo

git clone https://github.com/monicagangwar/docker-swarm-vagrant.git  
cd docker-swarm-vagrant  

Initialize VMs

Run vagrant up

• This will set up 3 VMs - manager, worker-1 & worker-2 all provisioned with docker
• manager node also has Flask app image monicagangwar/docker-swarm-vagrant installed on it.
  Which can be run as docker run -p 8000:8000 --name dsv monicagangwar/docker-swarm-vagrant

To ssh into the manager node run vagrant ssh manager
To ssh into worker node run vagrant ssh worker-1 or vagrant ssh worker-2

Initialize Swarm manager

• ssh into manager node
• run docker swarm init --advertise-addr <manager-IP-address>:2377
  IP address is of the Manager Virtual Machine. Can be found / setup in Vagrantfile
  Port 2377 is default for swarm
  This will generate a command with a token value docker swarm join --token <token> <manager-IP-address>:2377
• ssh into the worker nodes and execute the command generated above
• run docker node ls on the manager node to see the list of nodes and their roles(worker/manager)
• run docker network create -d overlay <network-name>
  creates an overlay network with the name specified which each of the container can join
  random-network will be the overlay network that our application containers live on
  -d tells which driver to use. Currently overlay driver is being used
• run docker service create --name <service-name> --network <network-name> <image-name>
  Creates the service with the given service name on the network specified. This will basically run containers from the image name specified on the nodes connected to the swarm.

Scale up and down

• Scale up : docker service update --replicas 7 <service-name>
  Replicates the container 7 times and balances into all available nodes based on a round-robin or any such algorithms. This will launch arbitrary number of containers in each node (including manager)
  Check which container is running on which node by running docker service ps <service-name>
  Check how many containers are running on the current node by running docker ps or docker container ls

• Scale down : docker service update --replicas 4 <service-name> This command will destroy some of the containers on some of the nodes. Check which containers got destroyed by using the commands specified above.

Manage worker nodes

• Drain : Bring a node down for management purpose
  docker node update --availability drain <worker-node-id>
  can be found by running docker node ls
  This will destroy the containers on the specified worker node and will relaunch them on available nodes

• Active : Bring up a node drained for management purpose
  docker node update --availability active <worker-node-id>
  This will activate the drained node and will deploy further scaled up containers on this as well

Helper commands

• docker service ls
  Lists the services created
• docker network ls
  Lists the networks created and available by default
• docker node ls
  Lists all the nodes in swarm
• docker service ps <service-name>
  Lists all the containers running in all swarm nodes.