Checks if the given key has a running, alive process in the cluster.

Ensures the process represented by key and child_spec is started, and it returns the pid of the process. In case of an unexpected problem it can return :undefined or nil.

Returns a :via tuple that represents the process behind the key.

Ths via tuple can be used in place of a process name, and it resolves to the pid behind key. To resolve it, you can use Paxtor.whereis/, or most of the standart OTP functions that take not only pids, but also process names, like GenServer.call.

There is no process started by just creating a via tuple, but resolving the via tuple (like Paxtor.whereis(via_tuple)) starts the process in case it was not started yet.

Returns the pid of the process behind key. If the process in not yet started, it starts the process using child_spec and returns the newly created pid.