Postgresql: replica and HA
The right way is setting hot-standby.

Using Repmgr is just a question of your convenience. You can use it, or you can setup trigger file creating, or promoting with pg_ctl, for example. It's your choice. Repmgr is not involved in process of streaming data from master to slave, it is just management tool.

Also,


Be careful with 'automatic promotion of slave in case of failing master'. You should definitely know what you are doing and you should define 'failing' very strictly. If you don't have a super-large cluster, then it is the best not to have failover fully automated.
Be careful about 'data loss'. You should know, that streaming replication will save you only in case there is some failure on server side, or something wrong with network/disk/etc. It won't help you if someone will come to your db and type DROP DATABASE. Changes from statements will be immediately streamed to slave and the DB will be lost everywhere. The only way to avoid data loss from SQL statements is a valid backup.