Problem

psql supports comma-separated hostnames for automatic failover:

psql -h "host1,host2,host3" -p 5432 -U postgres -c "SELECT 1"

rpg treats the entire comma-separated string as a single hostname, sends it to DNS, and fails.

Expected

rpg should parse comma-separated hosts and try each in sequence, connecting to the first that succeeds. This is standard libpq behavior and is commonly used for HA setups with a primary and one or more standbys.

psql docs reference

If host is a comma-separated list of host names, each will be tried in the given order.

Acceptance criteria

• -h "host1,host2" tries host1 first, falls back to host2
• PGHOST=host1,host2 same behavior
• host=host1,host2 in connstring same behavior
• postgres://host1,host2/db URI form same behavior
• Stops at first successful connection
• Error message lists all tried hosts if all fail

Discovered

Full connection matrix audit, 2026-03-24 (Section F, F5).