README: install PostgreSQL and configure Streaming Replication

Features:

• based on postgresql-on-el6 role.
• supported distributions:
  • RedHat, CentOS, Scientific Linux version 6 and 7
  • Oracle Linux also supported but uses RHEL repositories
  • Debian 8
  • Ubuntu 14.04
• supported PostgreSQL versions: 9.0, 9.1, 9.2, 9.3, 9.4, 9.5.
• allows specify users, and dedicated replication user and databases which would be created after install.
• ability to determine a set of postgresql.conf parameters and absense postgresql.conf template. Template is not used due to the fact that the postgresql.conf differs from version to version on a set of parameters.
• ability to specify another cluster directory and setup symlink into original data location.
• ability to specify extension list for created databases (only for versions >= 9.0).

Known issues:

• RHEL 6: packages from pgdg repo does not install due to repo configuration parsing error. Workaround: replace $releasever variable to your specific release version. This issue does not occurs on the others distributions.
• RHEL 6: posqtgresqlXY-contrib doesn't install due to dependency error. In my case, this may be caused by the use of an unregistered RedHat distribution and unofficial third-party repositories. On the Oracle Enterprise Linux this issue does not occur.

How-to use:

• specify postgresql_master boolean for master and slaves host or group variable or whatever:

[db-postgresql]
192.168.0.10 postgresql_master=true
192.168.0.11 postgresql_master=false
192.168.0.12 postgresql_master=false

• specify master and slaves ip addresses and other configuration in your variables:

postgresql_streaming_user:
  name: rep
  pass: secret
postgresql_streaming_master: 192.168.0.10
postgresql_streaming_slaves:
 - 192.168.0.11
 - 192.168.0.12

• set other relevant variables. (examples in defaults/main)
• important: sudo must be installed on remote machines.
• Run your playbook.

---
- name: Install and configure postgresql replica sets
  hosts: db-postgresql
  remote_user: root
  vars_files:
    - 'vars_postgresql.yml'
  roles:
    - { role: ansible-role-postgresql }