Swarm mode introduction

This tutorial will show you how to setup a swarm and deploy your first services.

Init your swarm

docker swarm init --advertise-addr $(hostname -i)

Copy the join command (watch out for newlines) output and paste it in the other terminal.

Show members of swarm

Type the below command in the first terminal:

docker node ls

That last line will show you a list of all the nodes, something like this:

ID                           HOSTNAME  STATUS  AVAILABILITY  MANAGE
R STATUS
kytp4gq5mrvmdbb0qpifdxeiv *  node1     Ready   Active        Leader
lz1j4d6290j8lityk4w0cxls5    node2     Ready   Active

If you try to execute an administrative command in a non-leader node worker, you’ll get an error. Try it here:

docker node ls

Creating services

The next step is to create a service and list out the services. This creates a single service called web that runs the latest nginx, type the below commands in the first terminal:

docker service create -p 80:80 --name web nginx:latest
docker service ls

You can check that nginx is running by executing the following command:

curl http://localhost:80

Scaling up

We will be performing these actions in the first terminal. Next let’s inspect the service:

docker service inspect web

That’s lots of info! Now, let’s scale the service:

docker service scale web=15

Docker has spread the 15 services evenly over all of the nodes

docker service ps web

Updating nodes

You can also drain a particular node, that is remove all services from that node. The services will automatically be rescheduled on other nodes.

docker node update --availability drain node2

docker service ps web

You can check out the nodes and see that node2 is still active but drained.

docker node ls

Scaling down

You can also scale down the service

docker service scale web=10

Lets check our service status

docker service ps web

Now bring node2 back online and show it’s new availability

docker node update --availability active node2

docker node inspect node2 --pretty

Which of these can you do with Docker Swarm Mode?