Momyre

Momyre — MOngo to MYsql simple REplicator — exists because I need to run SQL queries over data that only lives in a MongoDB cluster. Rather than rewrite the application, it’s a small Go daemon that mirrors Mongo collections into MySQL/MariaDB tables: it compares a YAML mapping config against what’s actually there, creates missing tables and columns, and folds Mongo arrays into JSON blobs where SQL has no equivalent.

It ships as a ~20MB Alpine Docker image and does the job.

The README carries a disclaimer: I’m not a database expert, and I don’t know whether replication is “perfectly safe” for anything sensitive. I wouldn’t recommend it for production use until you’ve proven it fits your needs with the right restrictions.