WAL-G slows down significantly when too many backups are kept. We need
to periodically clean up old backups to maintain a reasonable level of
performance, and also keep from wasting space with useless old backups.
`wal-g` needs to connect to the PostgreSQL database system, so it should
run as the _postgres_ user, who has permission to connect, rather than
_root_, who does not.
WAL archives are not much good without a base backup onto which they
can be applied. Thus, we need to schedule WAL-G to create and upload a
backup periodically.
This role installs `wal-g` from the DCH Yum repository, and creates a
configuration file for it in `/etc/postgresql`. Additionally, it
installs a custom SELinux policy module that allows `wal-g` to run in
the `postgresql_t` domain (i.e. when spawned by the PostgreSQL server).
Dustin