could not connect to the primary server: connection refused

Symptoms

A standby/replica could not connect to its primary server to stream WAL. The startup/walreceiver process reports SQLSTATE 08006 (connection_failure).

• The replica’s walreceiver cannot reach the primary.
• Replication stalls and the replica falls behind.
• Often a primary down, wrong primary_conninfo, or firewall.

What the server log shows

FATAL:  could not connect to the primary server: connection to server at "10.0.0.5", port 5432 failed: Connection refused

Why PostgreSQL raises this — what the manual says

Section 26.2 Log-Shipping Standby Servers (Streaming Replication):

“If you want to use streaming replication, fill in primary_conninfo with a libpq connection string, including the host name (or IP address) and any additional details needed to connect to the primary server.”

A streaming replica opens a replication connection to the primary defined by primary_conninfo. If that connection is refused (primary down, wrong host/port, firewall), the walreceiver cannot stream WAL and reports 08006.

Common causes

• The primary server is down or not accepting connections.
• Wrong host/port in primary_conninfo.
• Firewall/network blocking the replication port.

How to fix it

1. Verify the primary is up and listening on the replication port.
2. Check primary_conninfo host/port and credentials.
3. Open firewalls and confirm the replica can reach the primary.

Related & next steps

• SQLSTATE 08006 — Connection Failure (full reference)
• Message: connection to server was lost
• Glossary: Streaming replication

Reference: PostgreSQL 18 Section 27.2 “Log-Shipping Standby”.