When should I move a small Flask app from SQLite to PostgreSQL?

Some developers start with PostgreSQL in Docker even for small projects because it keeps local and hosted environments closer to each other. That’s a reasonable choice if you already know you’ll need multiple instances or PostgreSQL-specific features, but it isn’t required simply because the application is public.

Waiting for a measured problem is usually better than migrating just because SQLite has a reputation for being unsuitable for production. Set up monitoring for response times, database errors, connection problems, disk usage, and backup health. If one of those signals stays above a threshold, investigate and profile the application before changing the stack. Sometimes an index or a code fix solves the issue more cheaply than a database migration.

SQLite can absolutely be suitable for production, especially for a small application. The important question is whether your workload matches its limitations: the database is a local file, writes are serialized, and multiple application servers can’t safely share the same file. WAL mode can help with concurrent reads and writes. Consider moving when you need several app instances, frequent concurrent writes, or hosting with temporary storage that could lose the database during a redeploy.

Make the eventual migration easier now by using an ORM or a small data-access layer, keeping queries and database-specific logic in one place, and using schema migrations. Then moving to PostgreSQL later is much less disruptive. Just remember that an abstraction layer doesn’t hide every difference, so test important queries against the target database before switching.