Quick Dirty Postgresql Nspawn Container on Arch Linux

Refer to the Nspawn page for setting up the nspawn container.
And then refer the ArchWiki instructions for postgresql.

You'll want to install postgresql, set a password for the default user postgres, and then login as postgres and initilize the database.

pacman -S postgresql
# passwd for postgresql user 
passwd postgres 
# login as postgres 
su -l postgres
# initialize the databse cluster
[postgres]$ initdb --locale $LANG -E UTF8 -D '/var/lib/postgres/data'

You'll need to configure /var/lib/postgres/data/pg_hba.conf and /var/lib/postgres/data/postgresql.conf for remote access, presumably with an identd daemon in mind. The ident daemon will listen on port 113, not on the machine with the database server, but it listens from the machine where is the client that remotely wants to access the database.