Since we are using alpine linux we must install the alpine plugin for vagrant.
To make this easy for you you can run
$ ./init-vagrant.sh
When it's not your first run and there is no more a need to install docker you can just do vagrant up
$ vagrant up
ssh into one of the nodes
$ vagrant ssh manager-1
$ vagrant ssh manager-2
$ vagrant ssh node-1
$ vagrant ssh node-2
run the following command to initialize the 4 node swarm
./init-swarm.sh