Add prom metrics for database, use redis max conn var (#3359)

apps/labrinth/src/database/postgres_database.rs

@@ -1,4 +1,5 @@
 use log::info;
+use prometheus::{IntGauge, Registry};
 use sqlx::migrate::MigrateDatabase;
 use sqlx::postgres::{PgPool, PgPoolOptions};
 use sqlx::{Connection, PgConnection, Postgres};
@@ -45,3 +46,30 @@ pub async fn check_for_migrations() -> Result<(), sqlx::Error> {
 
     Ok(())
 }
+
+pub async fn register_and_set_metrics(
+    pool: &PgPool,
+    registry: &Registry,
+) -> Result<(), prometheus::Error> {
+    let pg_pool_size =
+        IntGauge::new("labrinth_pg_pool_size", "Size of Postgres pool")?;
+    let pg_pool_idle = IntGauge::new(
+        "labrinth_pg_pool_idle",
+        "Number of idle Postgres connections",
+    )?;
+
+    registry.register(Box::new(pg_pool_size.clone()))?;
+    registry.register(Box::new(pg_pool_idle.clone()))?;
+
+    let pool_ref = pool.clone();
+    tokio::spawn(async move {
+        loop {
+            pg_pool_size.set(pool_ref.size() as i64);
+            pg_pool_idle.set(pool_ref.num_idle() as i64);
+
+            tokio::time::sleep(Duration::from_secs(5)).await;
+        }
+    });
+
+    Ok(())
+}