prometheus metrics

fixes #1094
in progress

Cargo.toml

@@ -19,6 +19,7 @@ once_cell = "1.17.1"
 ott-common = { path = "crates/ott-common" }
 ott-balancer-protocol = { path = "crates/ott-balancer-protocol" }
 pin-project = "1.0.12"
+prometheus = "0.13.3"
 rand = "0.8.5"
 reqwest = { version = "0.11.17", features = ["json", "stream", "rustls-tls"] }
 serde = { version = "1", features = ["derive", "rc"] }

crates/ott-balancer-bin/Cargo.toml

@@ -33,4 +33,5 @@ ott-balancer-protocol.workspace = true
 route-recognizer = "0.3.1"
 once_cell.workspace = true
 pin-project.workspace = true
+prometheus.workspace = true
 trust-dns-resolver = { version = "0.22.0", features = ["system-config"] }

crates/ott-balancer-bin/src/service.rs

@@ -15,6 +15,7 @@ use reqwest::Url;
 use route_recognizer::Router;
 use tokio::sync::RwLock;
 use tracing::{debug, error, info, warn};
+use prometheus::{Opts, Registry, Counter, TextEncoder, Encoder};
 
 use crate::balancer::{BalancerContext, BalancerLink};
 use crate::client::client_entry;
@@ -83,7 +84,26 @@ impl Service<Request<IncomingBody>> for BalancerService {
                     .join("\n");
                     mk_response(rendered)
                 }
-                "metrics" => mk_response("TODO: prometheus metrics".to_owned()),
+                "metrics" => {
+                    // Create a Counter.
+                    let counter_opts = Opts::new("test_counter", "test counter help");
+                    let counter = Counter::with_opts(counter_opts).unwrap();
+
+                    // Create a Registry and register Counter.
+                    let r = Registry::new();
+                    r.register(Box::new(counter.clone())).unwrap();
+
+                    // Inc.
+                    counter.inc();
+
+                    // Gather the metrics.
+                    let mut buffer = vec![];
+                    let encoder = TextEncoder::new();
+                    let metric_families = r.gather();
+                    encoder.encode(&metric_families, &mut buffer).unwrap();
+
+                    mk_response(String::from_utf8(buffer).unwrap().to_owned())
+                },
                 "room" => {
                     let Some(room_name) = route.params().find("room_name") else {
                         return Ok(not_found());