Docker_Swarm

Docker Swarm
============

Should not run Docker containers on a single host.
 - for Production should use a cluster of docker hosts.

Docker Swarm enables you to manage all your docker instances as a single cluster.

Set up
------
1. Must have multiple hosts
2. Must designate one hosts to be a swarm manager or master.
3. Designate the others to be workers or slaves
4. Run the Docker Swarm init command on the master node.
5. Copy the docker swarm join command on the workers and they will join the cluster.
6. Deploy the service (images etc)

Deploy Services
---------------

Add new property call Deploy and specify the number of replicas to the
docker-compose.yaml file.

    deploy:
        replicas: 5

Example:

docker-compose.yml
-----------------------------
services:
     web:
        image: <name of repo = hub user>/<name of app>
        ports:
             - "80:5000"
                (external port: internal port)

        deploy:               ###################### added
            replicas: 5       ###################### added

     database:
         image: "mysql"

         volumes:
              - /opt/data:/var/lib/mysql
          (local host directory:directory inside container)


-----------------------------

Run or Deploy:
--------------

docker stack deploy -c docker-compose.yml (file name)

Load balancing covered elsewhere.