lemmy/src/prometheus_metrics.rs

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use actix_web::{rt::System, web, App, HttpResponse, HttpServer, Responder};
use lemmy_api_common::context::LemmyContext;
use lemmy_utils::settings::structs::PrometheusConfig;
use prometheus::{default_registry, Encoder, Gauge, Opts, TextEncoder};
use std::{
net::{IpAddr, Ipv4Addr},
sync::Arc,
thread,
};
struct PromContext {
lemmy: LemmyContext,
db_pool_metrics: DbPoolMetrics,
}
struct DbPoolMetrics {
max_size: Gauge,
size: Gauge,
available: Gauge,
}
static DEFAULT_BIND: IpAddr = IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1));
static DEFAULT_PORT: i32 = 10002;
pub fn serve_prometheus(config: Option<&PrometheusConfig>, lemmy_context: LemmyContext) {
let context = Arc::new(PromContext {
lemmy: lemmy_context,
db_pool_metrics: create_db_pool_metrics(),
});
let (bind, port) = match config {
Some(config) => (
config.bind.unwrap_or(DEFAULT_BIND),
config.port.unwrap_or(DEFAULT_PORT),
),
None => (DEFAULT_BIND, DEFAULT_PORT),
};
// spawn thread that blocks on handling requests
// only mapping /metrics to a handler
thread::spawn(move || {
let sys = System::new();
sys.block_on(async {
let server = HttpServer::new(move || {
App::new()
.app_data(web::Data::new(Arc::clone(&context)))
.route("/metrics", web::get().to(metrics))
})
.bind((bind, port as u16))
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.unwrap_or_else(|_| panic!("Cannot bind to {}:{}", bind, port))
.run();
if let Err(err) = server.await {
eprintln!("Prometheus server error: {}", err);
}
})
});
}
// handler for the /metrics path
async fn metrics(context: web::Data<Arc<PromContext>>) -> impl Responder {
// collect metrics
collect_db_pool_metrics(&context).await;
let mut buffer = Vec::new();
let encoder = TextEncoder::new();
// gather metrics from registry and encode in prometheus format
let metric_families = prometheus::gather();
encoder.encode(&metric_families, &mut buffer).unwrap();
let output = String::from_utf8(buffer).unwrap();
HttpResponse::Ok().body(output)
}
// create lemmy_db_pool_* metrics and register them with the default registry
fn create_db_pool_metrics() -> DbPoolMetrics {
let metrics = DbPoolMetrics {
max_size: Gauge::with_opts(Opts::new(
"lemmy_db_pool_max_connections",
"Maximum number of connections in the pool",
))
.unwrap(),
size: Gauge::with_opts(Opts::new(
"lemmy_db_pool_connections",
"Current number of connections in the pool",
))
.unwrap(),
available: Gauge::with_opts(Opts::new(
"lemmy_db_pool_available_connections",
"Number of available connections in the pool",
))
.unwrap(),
};
default_registry()
.register(Box::new(metrics.max_size.clone()))
.unwrap();
default_registry()
.register(Box::new(metrics.size.clone()))
.unwrap();
default_registry()
.register(Box::new(metrics.available.clone()))
.unwrap();
metrics
}
async fn collect_db_pool_metrics(context: &PromContext) {
let pool_status = context.lemmy.pool().status();
context
.db_pool_metrics
.max_size
.set(pool_status.max_size as f64);
context.db_pool_metrics.size.set(pool_status.size as f64);
context
.db_pool_metrics
.available
.set(pool_status.available as f64);
}