Fixing DBAPI Connection Failures When localhost and IP Behave Differently

Database connection issues under FastCGI can become confusing when the same credentials behave differently depending on whether the host is specified as localhost or an IP address. That difference is not cosmetic: it can change socket behavior, resolution paths, and how the runtime reaches MySQL.

The practical takeaway is that DBAPI connection testing should include the transport assumption itself. If one host form fails while another works, the problem may be in how PHP and the server stack resolve local database access rather than in the username or password alone.

This is a good Best Practices topic because those environment-specific mismatches are common on older Evolution stacks and can waste a lot of debugging time if you treat them as ordinary credential errors.