pgbackrest with PAF(corosync and pacmaker)

##Arch
OS: Centos 7
PostgreSQL 10
pgbackrest 2.18
PAF: two nodes(primary and secondary ) with corosync and pacemaker

##Query
I am using pacemaker and corosync to setup two nodes High availability
cluster for postgreSQL 10. In the scenario I want to setup timely backup
with pgbackrest.
Using the _backup from standby_ feature I could able to take backup from my
secondary postgres. But if secondary postgres is down, it does not take
backup from primary.

What I want?
I want to take backup from secondary postgres (--backup-standby), If
secondary is unavailable, take backup from primary postgres.
Or if Primary postgres goes down backup should still continues from
secondary (which would have been promoted to master now)

All backups are with remote repository
pgbackrest.conf for repo:

*[data]pg1-host=pgprimarypg1-path=/var/lib/pgsql/10/datapg2-host=pgsecpg2-path=/var/lib/pgsql/10/data[global]backup-standby=yprocess-max=3repo1-path=/var/lib/pgbackrestrepo1-retention-full=2start-fast=y*

pgbackrest for primary and secondary postgres:

*[data]pg1-host=mainpg1-path=/var/lib/pgsql/10/datapg2-host=secpg2-path=/var/lib/pgsql/10/data[global]backup-standby=nprocess-max=3repo1-path=/var/lib/pgbackrestrepo1-retention-full=2start-fast=y*

Is there any way to achieve this?
This sounds like a generic problem? Or am I doing something wrong

Regards,
ajay

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