Feature/pg rewind unclean shutdown. Allow pg_rewind to rewind the former master if it was uncleanly shutdown or just lost the connection and advanced past the point where the new master had promoted. Add configuration block pg_rewind with username and password as mandatory parameters inside this block.
Implement callback actions for patroni in order to call external script on different events in the server lifecycle, supported are on start, stop, restart, reload and role change (which covers both promote and demote). A callback should receive 3 arguments: action, role and cluster name (in this order), and can do things like tagging the EC2 instances associated with PostgreSQL, or notifying the DBA when the master had been demoted.
A sample callback that assigns tags to AWS instances is provided.
Oleksii Kliukin