host_url
relies on using the host name of the computer
rather than an IP address and typically works on local networks, although
this is not always guaranteed. If unsuccessful, substitute an IPv4 or
IPv6 address in place of the hostname.
local_url
generates a random URL for the platform's default
inter-process communications transport: abstract Unix domain sockets on
Linux, Unix domain sockets on MacOS, Solaris and other POSIX platforms,
and named pipes on Windows.