Context
PostgreSQL host-based authentication rules are evaluated in order. The first row matching the connection type, client address, database, and role selects the authentication method. If authentication fails there, PostgreSQL does not continue looking for a more convenient row. This explains why adding a permissive line at the bottom often changes nothing.
Establish the real connection
Collect the server version, effective client address, requested database and role, SSL use, and exact sanitized error. Identify proxies, connection poolers, and address translation that can change what the server sees. Obtain access to the active HBA file and its inspection view. Keep an established administrator session while preparing access changes, and use a controlled test connection for verification.
Trace rule selection
- Find the actual configuration location with
SHOW hba_filewhere your hosting environment permits it. Review includes as well as the main file. A familiar path on disk may not belong to the running cluster. Confirm that the incident reaches the intended PostgreSQL instance before editing any policy. - Inspect
pg_hba_file_rulesfor row order and non-null error fields. The view helps identify malformed records in the file, but successful parsing alone does not prove that a particular connection will be accepted. Read included rules in effective order and compare the intended role and database names precisely. - Work through the real connection attributes from the top. Distinguish local socket connections from TCP, and encrypted TCP from unencrypted TCP where
hostsslorhostnosslis involved. Match the address PostgreSQL observes, not necessarily the address displayed on the application host. Stop at the first matching rule and inspect that authentication method. - Prepare the smallest correct rule change and apply the documented configuration reload procedure for your operating system and service. Preserve a rollback copy. Test a new connection from the real application path, then test a representative connection that should remain denied. Existing sessions do not reauthenticate when the file is reloaded.
Diagnostic table
| Symptom | Likely explanation | Evidence |
|---|---|---|
| New bottom rule has no effect | Earlier row matches first | Effective HBA order |
| Laptop works, application fails | Different address or transport | Server-observed connection attributes |
| Parse error appears in rule view | Invalid file entry | Error text and line reference |
| Reload succeeds, old pool still works | Existing sessions hide change | Fresh connection result |
Illustrative scenario
An application connects through a pooler, so PostgreSQL sees the pooler's address. An operator adds a rule for the application subnet, but the pooler's connection continues matching an earlier password rule. The team documents both hops, revises the intended pooler rule narrowly, and tests a newly opened backend connection. The client-side subnet was relevant to the first hop but not to PostgreSQL's HBA selection.
Correct and verify
If the selected row is correct but authentication fails, investigate credentials or client authentication support instead of broadening the address range. If no row matches, correct the intended tuple rather than using an unrestricted trust rule. Verify both successful and denied cases after reload and after a pool restart in staging. Keep sanitized results with the exact policy revision.
Operating procedure
Review HBA entries with owners, purpose, and expiry for temporary access. Monitor denied connections without retaining passwords. Include proxy addresses and transport requirements in network diagrams. During upgrades or authentication migrations, recheck rule selection before diagnosing driver failures, since the chosen row determines which authentication path the driver must support.
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