Getting Started with Node Labels In Docker Swarm

List your current nodes.
```
docker node ls
```

Add a label to a node.

docker node update --label-add availability_zone=east <NODE_NAME>
docker node update --label-add availability_zone=west <NODE_NAME>

View existing labels with:

docker node inspect --pretty <NODE_NAME>

You can use --constraint when creating a service to restrict which nodes will be used to execute a service’s tasks.

docker service create --name nginx-east --constraint node.labels.availability_zone==east --replicas 3 nginx
docker service ps nginx-east
docker service create --name nginx-west --constraint node.labels.availability_zone!=east --replicas 3 nginx
docker service ps nginx-west

Use --placement-pref to spread tasks evenly based on the value of a specific label.

docker service create --name nginx-spread --placement-pref spread=node.labels.availability_zone --replicas 3 nginx
docker service ps nginx-spread