feat(db): add read-replica pool routing with Prometheus metrics - #1096
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chinweobtagaz merged 1 commit intoAug 26, 2026
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- Add DbPool struct (backend/modules/db/src/db.rs) wrapping primary
(read-write) and replica (read-only) sea-orm DatabaseConnection pools.
Gracefully falls back to single-pool mode when DATABASE_REPLICA_URL
is unset — server never crashes on startup without a replica.
- Export DbPool from db crate root (db::DbPool).
- Add Prometheus gauges: db_pool_connections_{active,idle,max} with
a 'pool' label ('primary' | 'replica'). Exposed at GET /metrics.
- Refactor GameService (service/games.rs): all read methods
(get_game, list_games, get_game_history, get_player_rating_for_game)
route to replica; all write/transactional methods (create_game,
make_move, join_game, abandon_game, import_game, complete_game)
route to primary.
- Refactor PlayerService (service/players.rs): reads (find_player_by_id,
get_player_by_username, authenticate_player) route to replica; writes
(add_player, update_player, delete_player) route to primary.
- Update api handlers (games.rs, players.rs, auth.rs, server.rs) to
accept web::Data<DbPool> instead of web::Data<DatabaseConnection>.
Auth token writes (generate, rotate, revoke) go to primary; player
lookup on login goes to replica.
- Add /metrics endpoint to server.rs that snapshots pool stats and
returns Prometheus text format.
- Add integration tests validating read/write pool routing using
MockDatabase (db/src/integration_tests.rs,
service/src/routing_tests.rs). Live-DB smoke tests skip gracefully
when DATABASE_URL is absent.
- Document DATABASE_REPLICA_URL in .env.example.
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Add DbPool struct (backend/modules/db/src/db.rs) wrapping primary (read-write) and replica (read-only) sea-orm DatabaseConnection pools. Gracefully falls back to single-pool mode when DATABASE_REPLICA_URL is unset — server never crashes on startup without a replica.
Export DbPool from db crate root (db::DbPool).
Add Prometheus gauges: db_pool_connections_{active,idle,max} with a 'pool' label ('primary' | 'replica'). Exposed at GET /metrics.
Refactor GameService (service/games.rs): all read methods (get_game, list_games, get_game_history, get_player_rating_for_game) route to replica; all write/transactional methods (create_game, make_move, join_game, abandon_game, import_game, complete_game) route to primary.
Refactor PlayerService (service/players.rs): reads (find_player_by_id, get_player_by_username, authenticate_player) route to replica; writes (add_player, update_player, delete_player) route to primary.
Update api handlers (games.rs, players.rs, auth.rs, server.rs) to accept web::Data instead of web::Data. Auth token writes (generate, rotate, revoke) go to primary; player lookup on login goes to replica.
Add /metrics endpoint to server.rs that snapshots pool stats and returns Prometheus text format.
Add integration tests validating read/write pool routing using MockDatabase (db/src/integration_tests.rs, service/src/routing_tests.rs). Live-DB smoke tests skip gracefully when DATABASE_URL is absent.
Document DATABASE_REPLICA_URL in .env.example.
closes #1027