> We use Barman inside Kubernetes via CloudNativePG's plugin, as it is the default backup plugin.

right and here's why CloudNativePG chose Barman over pgBackRest: https://github.com/cloudnative-pg/cloudnative-pg/issues/3077

> WAL limits need to be set carefully or you just end up filling WAL volumes and the database becoming unavailable.

This is true. For anyone getting alarmed that this is due to a bug in PostgreSQL, it's not - it's PostgreSQL protecting the customer from attempting to write data that it cannot durable commit - "I am going to go unavailable because I don't have enough space to save more data".

There are multiple ways to handle this, the easiest, most hands on way is to keep a monitor and alert that watches the WAL size like a hawk and then alerts OPS the moment it breaches a threshold.