Status can be checked with the query
select * from pg_stat_replication. The repl field is helpful in verifying the status of the PostgreSQL instances. If the repl field exists, it means that the node’s standby is caught up and streaming. If there is no repl field, it means that there is no Postgres instance replication from this node.
Links
PostgreSQL: Documentation: 9.6: Write Ahead Log: https://www.postgresql.org/docs/9.6/runtime-config-wal.html
PostgreSQL: Documentation: 9.6: Log-Shipping Standby Servers: https://www.postgresql.org/docs/9.6/warm-standby.html#CASCADING-REPLICATION
PostgreSQL: Documentation: 9.6: Routine Vacuuming: https://www.postgresql.org/docs/9.6/routine-vacuuming.html#AUTOVACUUM
PostgreSQL: Documentation: 9.6: Replication: https://www.postgresql.org/docs/9.6/runtime-config-replication.html#RUNTIME-CONFIG-REPLICATION-STANDBY
Joyent Triton example
https://github.com/joyent/sdc-manatee/tree/master/etc/9.6
https://github.com/joyent/sdc-manatee/blob/master/bin/manatee-backup.sh