Locale and encoding

Mastodon requires these manual steps:

su - postgres
psql postgres

ALTER USER mastodon CREATEDB;
UPDATE pg_database SET datistemplate = FALSE WHERE datname = 'template1';
DROP DATABASE template1;
CREATE DATABASE template1 WITH TEMPLATE = template0 ENCODING = 'UNICODE';
UPDATE pg_database SET datistemplate = TRUE WHERE datname = 'template1';
\c template1
VACUUM FREEZE;

Synapse requires:

su - postgres
# Or, if your system uses sudo to get administrative rights
sudo -u postgres bash

Then, create a postgres user and a database with:

# this will prompt for a password for the new user
createuser --pwprompt synapse_user

createdb --encoding=UTF8 --locale=C --template=template0 --owner=synapse_user synapse

The above will create a user called synapse_user, and a database called synapse.

Additional options from community.postgresql.postgresql_db module should be added to this role.