flynn-host is the Flynn host service. An instance of it runs on every host in
the Flynn cluster. It is responsible for running jobs (in Linux containers) and
reporting back to schedulers and the leader.
flynn-host is capable of bootstrapping itself inside of containers with its dependencies using the included manifest. It depends on discoverd, which in turn depends on etcd. These three components are referred to as "Layer 0".
One instance of host acts as the "cluster leader" and serializes the creation of new jobs. The leader is maintains the entire cluster state (a list of hosts and their running jobs) in memory. If the leader disappears, a new one is elected by discoverd and the rest of the hosts connect to it and provide their current state.