wal-g backup-push tries to use wrong database

When trying to use wal-g with Patroni, I've got the following configuration as the Postgres section of patroni.yml:

postgresql:
  use_pg_rewind: true
  use_slots: true
  parameters:
    wal_level: logical
    hot_standby: "on"
    wal_keep_segments: 8
    max_wal_senders: 8
    max_replication_slots: 8
    checkpoint_timeout: 30
    archive_mode: "on"
    archive_command: PGUSER=dba PGPASSWORD=xx WALG_FILE_PREFIX=file://localhost/backup-disk/ wal-g wal-push "%p"
  recovery_conf:
    restore_command: PGUSER=dba PGPASSWORD=xx WALG_FILE_PREFIX=file://localhost/backup-disk/ wal-g wal-fetch "%f" "%p"

However if I then try to create a backup using PGHOST=/var/run/postgresql PGUSER=dba PGPASSWORD=xx envdir /data/conf/wal-e.env wal-g backup-push /data/postgresql/current, it tries to connect to the dba database which doesn't exist:

INFO:  Doing full backup.
ERROR: Connect: postgres connection failed: FATAL: database "dba" does not exist (SQLSTATE 3D000)

From the wal-g docs and searching, it's not obvious why this is not the case, so in an attempt to make things more discoverable I'm asking the question.

Solution

The answer turned out to be quite simple once I checked out the WAL-G source code and found that examples of their environment config for their tests contained the following setting:

PGDATABASE=postgres

So to have a backup apparently work, I now have the following:

PGDATABASE=postgres PGHOST=/var/run/postgresql PGUSER=dba PGPASSWORD=xx WALG_FILE_PREFIX=file://localhost/backup-disk/ wal-g backup-push /data/postgresql/current

This creates the expected files in /backup-disk/, so now all I need to do is sort out scheduling some backups of the correct database.