Hydra is a distributed emulation framework for large-scale software testing in disrupted networks. The Hydra Slave is the distributed component on virtualization hosts which performs the preparation and maintainance of the nodes.
In most set-ups all the nodes should be connected to each other. One way to do that is to create a bridged interface using the bridge tools.
sudo brctl addbr sim-br0
sudo ifconfig sim-br0 up
Then configure the basic slave.properties according to your needs.
To start the slave just call the python interpreter.
python src/default.py -c slave.properties