Jenkins Swarm can't connect to master

I've got an AWS linux master and an AWS linux slave for Jenkins. They are both in the same security group and have all TCP ports open to each other. Because the slave will be turned on and off, the IP changes quite often, which stops me from being able to ssh into it. I've looked at Swarm and haven't had any luck.

I installed and started Jenkins as yum install jenkins and service jenkins start which means it's running as a service.

On the slave I downloaded swarm client and an running:

$ java -jar swarm-client-1.8-jar-with-dependencies.jar -name yoshi -executors 1 -fsroot /var/lib/jenkins -labels linux -master http://<master_ip>:8080/jenkins -username jenkins -password <PASSWORD>

The output is:

Discovering Jenkins master
Failed to fetch slave info from Jenkins CODE: 404
Retrying in 10 seconds

Any ideas why I'm getting a 404 or how to do this the right way?