# TYPE  DATABASE        USER            ADDRESS                 METHOD
local   all             pgsql                                   peer
local   all             all                                     md5
host    all             all             127.0.0.1/32            md5
host    all             all             ::1/128                 md5

$ su pgsql
$ psql template1
template1=# l
                         List of databases
...

- name: Create the postgresql database
  postgresql_db: name=mydatabase login_user=pgsql

PLAY [web] ********************************************************************

GATHERING FACTS ***************************************************************
ok: [host.example.org]

TASK: [database | Create the postgresql database] *****************************
failed: [host.example.org] => {"failed": true}
msg: unable to connect to database: FATAL:  Peer authentication failed for user "pgsql"


FATAL: all hosts have already failed -- aborting

- name: Create postgres database
  become: true
  become_user: postgres
  postgresql_db:
    name: <database-name>

- name: Create postgres user
  postgresql_user: name={{ pg_user }} password={{ pg_password }}
  become: true
  become_user: postgres

- name: Create the postgresql database
  remote_user: pgsql
  postgresql_db: name=mydatabase login_user=pgsql
  ...

- name: Create the postgresql database
  remote_user: root
  become: yes
  become_user: pgsql
  postgresql_db: name=mydatabase login_user=pgsql
  ...

[ssh_connection]
pipelining=True