Why SQLite instead of Postgres/Redis?

[Janady13]

The sidecar is a single-machine service. SQLite at /var/lib/seo-sidecar/schemas.db is fast (sub-ms writes), durable (WAL mode), and zero-config.

Postgres adds an external dependency. The sidecar would have to handle Postgres connection lifecycle, retries, failover. Schemas are small (a few KB each), update rates are low (push when content changes — minutes, not milliseconds), so the throughput advantage of Postgres doesn't matter here.

Redis adds another external dependency AND doesn't give you durable persistence by default. Schemas should survive a reboot without manual replay.

If you have 50+ nginx hosts and want a centralized schema store, swap SQLite for Postgres in sidecar.py — it's ~20 lines of code. The endpoint shape doesn't change.