pg_hba.conf entry query I'm trying to formulate a rule from pg_hba.conf file. Thus far I have understood that pg_hba.conf file is used to give access to the specific user for a specific host. But I just want to take a second opinion hence this question.

Given that I defined a set of entry in pg_hba.conf:

# IPv4 local connections:
host    all             all             127.0.0.1/32            md5
# IPv6 local connections:
host    all             all             ::1/128                 md5

host    all            all             111.121.10.32/32         md5


Then does Postgres guarantee the only way anyone can connect to Postgres is either using localhost or from 111.121.10.32 and not other IP will be able to access the Postgres server.

Is my understanding correct?
Your understanding is correct. For every connection attempt, each line in pg_hba.conf is checked in turn. The first matching line applies and the connection then either passes with this or fails trying. Much like a firewall. The manual:


  The first record with a matching connection type, client address, requested database, and user name is used to perform authentication. There is no “fall-through” or “backup”: if one record is chosen and the authentication fails, subsequent records are not considered. If no record matches, access is denied.


Bold emphasis mine.