Added monitoring, limited concurent connections (#245)

* reduced the default, and added environment override.

* Using parse is more stable and doesn't fail CI this time :P

* Added support for monitoring
This support is currently basic, but it can be improved later down the road.

* Forgot scheduler file

* Added health check

* Cargo fix

* Update cargo.lock to avoid action fails.

Co-authored-by: Geometrically <18202329+Geometrically@users.noreply.github.com>

src/health/scheduler.rs

@@ -0,0 +1,127 @@
+use crate::scheduler::Scheduler;
+use sqlx::{Pool, Postgres};
+
+use prometheus::{opts, IntGaugeVec};
+use actix_web::dev::{Service, ServiceRequest, ServiceResponse, Transform};
+use actix_web::Error;
+
+use std::pin::Pin;
+use std::future::{Future};
+use std::task::{Context, Poll};
+use futures::future::{ok, Ready};
+
+use crate::health::pod::PodInfo;
+use actix_web::http::{HeaderName, HeaderValue};
+use actix_web_prom::{PrometheusMetrics};
+
+pub struct HealthCounters {
+    pod: PodInfo,
+    idle_db_conn: IntGaugeVec,
+    opened_db_conn: IntGaugeVec,
+    current_requests: IntGaugeVec,
+}
+impl HealthCounters {
+    pub fn new() -> Self {
+        let idle_opts = opts!("idle_db_conn", "Amount of idle connections").namespace("api");
+        let opened_opts = opts!("open_db_conn", "Amount of open connections").namespace("api");
+        let current_opts = opts!("current_requests", "Currently open requests").namespace("api");
+        Self {
+            pod: PodInfo::new(),
+            idle_db_conn: IntGaugeVec::new(idle_opts, &[]).unwrap(),
+            opened_db_conn: IntGaugeVec::new(opened_opts, &[]).unwrap(),
+            current_requests: IntGaugeVec::new(current_opts, &["endpoint", "method"]).unwrap(),
+        }
+    }
+    pub fn register(&self, builder: &mut PrometheusMetrics) {
+        builder
+            .registry
+            .register(Box::new(self.opened_db_conn.clone())).unwrap();
+        builder
+            .registry
+            .register(Box::new(self.idle_db_conn.clone())).unwrap();
+        builder
+            .registry
+            .register(Box::new(self.current_requests.clone())).unwrap();
+    }
+    pub fn schedule(&self, pool: Pool<Postgres>, scheduler: &mut Scheduler) {
+        let this = self.clone();
+        scheduler.run(std::time::Duration::from_secs(5), move || {
+            let idle = pool.num_idle();
+            let total = pool.size();
+            this.idle_db_conn.with_label_values(&[]).set(idle as i64);
+            this.opened_db_conn.with_label_values(&[]).set(total as i64);
+            async move {
+                ok::<i32, i32>(1).await.unwrap();
+            }
+        });
+    }
+}
+
+impl Clone for HealthCounters {
+    fn clone(&self) -> Self {
+        Self {
+            pod: self.pod.clone(),
+            idle_db_conn: self.idle_db_conn.clone(),
+            opened_db_conn: self.opened_db_conn.clone(),
+            current_requests: self.current_requests.clone(),
+        }
+    }
+}
+
+impl<S, B> Transform<S> for HealthCounters
+    where
+        S: Service<Request = ServiceRequest, Response = ServiceResponse<B>, Error = Error>,
+        S::Future: 'static,
+        B: 'static,
+{
+    type Request = ServiceRequest;
+    type Response = ServiceResponse<B>;
+    type Error = Error;
+    type Transform = MonitoringMiddleware<S>;
+    type InitError = ();
+    type Future = Ready<Result<Self::Transform, Self::InitError>>;
+
+    fn new_transform(&self, service: S) -> Self::Future {
+        ok(MonitoringMiddleware { service, counters: self.clone() })
+    }
+}
+
+
+
+
+pub struct MonitoringMiddleware<S> {
+    service: S,
+    counters: HealthCounters,
+}
+
+impl<S, B> Service for MonitoringMiddleware<S>
+    where
+        S: Service<Request = ServiceRequest, Response = ServiceResponse<B>, Error = Error>,
+        S::Future: 'static,
+        B: 'static,
+{
+    type Request = ServiceRequest;
+    type Response = ServiceResponse<B>;
+    type Error = Error;
+    type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>>>>;
+
+    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        self.service.poll_ready(cx)
+    }
+
+    fn call(&mut self, req: ServiceRequest) -> Self::Future {
+        // The request has started.
+        let pattern_or_path = req.match_pattern().unwrap_or("unknown".to_string());
+        let counter = self.counters.current_requests.with_label_values(&[&*pattern_or_path,req.method().as_str()]);
+        counter.inc();
+        let pod = self.counters.pod.clone();
+        let fut = self.service.call(req);
+        Box::pin(async move {
+            let mut res: Self::Response = fut.await?;
+            // The request finished, remove a counter
+            counter.dec();
+            res.headers_mut().insert(HeaderName::from_static("x-server"), HeaderValue::from_str(&*pod.get_id()).unwrap());
+            Ok(res)
+        })
+    }
+}