mirror of https://github.com/LemmyNet/lemmy
Add Prometheus endpoint (#3456)
Add a server for serving Prometheus metrics. Include a configuration block in the config file. Provide HTTP metrics on the API, along with process-level metrics and DB pool metrics.pull/3482/head
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use actix_web::{rt::System, web, App, HttpResponse, HttpServer, Responder};
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use lemmy_api_common::context::LemmyContext;
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use lemmy_utils::settings::structs::PrometheusConfig;
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use prometheus::{default_registry, Encoder, Gauge, Opts, TextEncoder};
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use std::{
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net::{IpAddr, Ipv4Addr},
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sync::Arc,
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thread,
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};
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struct PromContext {
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lemmy: LemmyContext,
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db_pool_metrics: DbPoolMetrics,
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}
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struct DbPoolMetrics {
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max_size: Gauge,
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size: Gauge,
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available: Gauge,
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}
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static DEFAULT_BIND: IpAddr = IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1));
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static DEFAULT_PORT: i32 = 10002;
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pub fn serve_prometheus(config: Option<&PrometheusConfig>, lemmy_context: LemmyContext) {
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let context = Arc::new(PromContext {
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lemmy: lemmy_context,
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db_pool_metrics: create_db_pool_metrics(),
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});
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let (bind, port) = match config {
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Some(config) => (
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config.bind.unwrap_or(DEFAULT_BIND),
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config.port.unwrap_or(DEFAULT_PORT),
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),
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None => (DEFAULT_BIND, DEFAULT_PORT),
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};
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// spawn thread that blocks on handling requests
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// only mapping /metrics to a handler
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thread::spawn(move || {
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let sys = System::new();
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sys.block_on(async {
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let server = HttpServer::new(move || {
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App::new()
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.app_data(web::Data::new(Arc::clone(&context)))
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.route("/metrics", web::get().to(metrics))
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})
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.bind((bind, port as u16))
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.expect(&format!("Cannot bind to {}:{}", bind, port))
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.run();
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if let Err(err) = server.await {
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eprintln!("Prometheus server error: {}", err);
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}
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})
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});
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}
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// handler for the /metrics path
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async fn metrics(context: web::Data<Arc<PromContext>>) -> impl Responder {
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// collect metrics
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collect_db_pool_metrics(&context).await;
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let mut buffer = Vec::new();
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let encoder = TextEncoder::new();
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// gather metrics from registry and encode in prometheus format
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let metric_families = prometheus::gather();
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encoder.encode(&metric_families, &mut buffer).unwrap();
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let output = String::from_utf8(buffer).unwrap();
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HttpResponse::Ok().body(output)
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}
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// create lemmy_db_pool_* metrics and register them with the default registry
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fn create_db_pool_metrics() -> DbPoolMetrics {
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let metrics = DbPoolMetrics {
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max_size: Gauge::with_opts(Opts::new(
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"lemmy_db_pool_max_connections",
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"Maximum number of connections in the pool",
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))
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.unwrap(),
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size: Gauge::with_opts(Opts::new(
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"lemmy_db_pool_connections",
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"Current number of connections in the pool",
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))
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.unwrap(),
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available: Gauge::with_opts(Opts::new(
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"lemmy_db_pool_available_connections",
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"Number of available connections in the pool",
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))
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.unwrap(),
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};
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default_registry()
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.register(Box::new(metrics.max_size.clone()))
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.unwrap();
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default_registry()
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.register(Box::new(metrics.size.clone()))
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.unwrap();
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default_registry()
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.register(Box::new(metrics.available.clone()))
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.unwrap();
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return metrics;
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}
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async fn collect_db_pool_metrics(context: &PromContext) {
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let pool_status = context.lemmy.pool().status();
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context
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.db_pool_metrics
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.max_size
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.set(pool_status.max_size as f64);
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context.db_pool_metrics.size.set(pool_status.size as f64);
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context
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.db_pool_metrics
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.available
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.set(pool_status.available as f64);
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}
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