Resolving PgBouncer SCRAM and MD5 Authentication Mismatches

Have you ever updated a PostgreSQL user password, only to have your PgBouncer logs explode with FATAL: server login has been failing? If you’re seeing this error—or the dreaded (nouser) connection drop—you aren’t alone. It’s a common pitfall when migrating authentication methods.

This issue typically stems from a mismatch between SCRAM-SHA-256 and MD5 encryption settings. Even if your backend database is perfectly healthy, a simple configuration gap in your userlist.txt or pgbouncer.ini can stop your entire connection pool in its tracks.

In this walkthrough, we break down why this happens and provide two clear paths to recovery:

The "Revert" Method: How to temporarily roll back to MD5 if you need immediate service restoration and don't have time for a full security migration.

The "Upgrade" Method: How to correctly configure PgBouncer for modern, secure SCRAM-SHA-256 authentication, ensuring your infrastructure is up to date.

Whether you are an SRE, a Database Administrator, or just a developer trying to get your service back online, this guide provides the exact commands you need to align your authentication types and stop the login loops.

In this guide, you’ll learn:

How to diagnose server_login_retry errors in PgBouncer logs.

Why auth_type must match your user password encryption.

Step-by-step instructions for updating userlist.txt and re-extracting database secrets.

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