Locking and Unlocking a Swarm Cluster

Enable autolock.
```
docker swarm update --autolock=true
```
Make note of the unlock key!
Run a command to interact with the swarm, then restart docker and try the command again to verify that the swarm is locked.
```
docker node ls
sudo systemctl restart docker
docker node ls
```
Unlock the swarm using the unlock key and verify that it is unlocked.
```
docker swarm unlock
docker node ls
```
Obtain the existing unlock key.
```
docker swarm unlock-key
```
Rotate the unlock key.
```
docker swarm unlock-key --rotate
```

Disable autolock.

docker swarm update --autolock=false
sudo systemctl restart docker
docker node ls