prometheus
Histogram with empty family labels creates unparseable metrics output
I'm loosely following the actix example to add prom metrics for my simple webapp which doesn't need additional family labels on its metrics for now. However, when I tried removing the family labels, I get unparseable output from the metrics endpoint:
$ curl localhost:8080/metrics
# HELP requests Count of requests.
# TYPE requests counter
requests_total{} 1
# HELP elapsed Histogram of elapsed.
# TYPE elapsed histogram
elapsed_sum{} 10.0
elapsed_count{} 1
elapsed_bucket{le="0.0",} 0
elapsed_bucket{le="+Inf",} 1
# EOF
The extra comma in the label list for each bucket causes this to be unparseable by prometheus, resulting in the following error:
expected label name, got "BCLOSE"
Is this intended behavior? Or is there a better way to create metrics without family labels? I boiled my issue down to a small app which I'll include below, along with a test case and patch that I've found fixes the issue for me locally. I'd be happy to submit a PR with the fix if desired.
Test app source:
use std::sync::Mutex;
use actix_web::{web, App, HttpResponse, HttpServer, Responder, Result};
use prometheus_client::encoding::text::encode;
use prometheus_client::metrics::counter::Counter;
use prometheus_client::metrics::family::Family;
use prometheus_client::metrics::histogram::{Histogram, linear_buckets};
use prometheus_client::registry::Registry;
pub struct Metrics {
requests: Family<(), Counter>,
elapsed: Family<(), Histogram>,
}
pub struct AppState {
pub registry: Registry,
}
pub async fn metrics_handler(state: web::Data<Mutex<AppState>>) -> Result<HttpResponse> {
let state = state.lock().unwrap();
let mut body = String::new();
encode(&mut body, &state.registry).unwrap();
Ok(HttpResponse::Ok()
.content_type("application/openmetrics-text; version=1.0.0; charset=utf-8")
.body(body))
}
pub async fn some_handler(metrics: web::Data<Metrics>) -> impl Responder {
metrics.requests.get_or_create(&()).inc();
metrics.elapsed.get_or_create(&()).observe(10f64);
"okay".to_string()
}
#[actix_web::main]
async fn main() -> std::io::Result<()> {
let elapsed_hist: Family<(), Histogram> = Family::new_with_constructor(||
Histogram::new(linear_buckets(0f64, 1f64, 1)));
let metrics = web::Data::new(Metrics {
requests: Family::default(),
elapsed: elapsed_hist,
});
let mut state = AppState {
registry: Registry::default(),
};
state
.registry
.register("requests", "Count of requests", metrics.requests.clone());
state
.registry
.register("elapsed", "Histogram of elapsed", metrics.elapsed.clone());
let state = web::Data::new(Mutex::new(state));
HttpServer::new(move || {
App::new()
.app_data(metrics.clone())
.app_data(state.clone())
.service(web::resource("/metrics").route(web::get().to(metrics_handler)))
.service(web::resource("/handler").route(web::get().to(some_handler)))
})
.bind(("127.0.0.1", 8080))?
.run()
.await
}
Output:
$ curl localhost:8080/handler; curl localhost:8080/metrics
okay# HELP requests Count of requests.
# TYPE requests counter
requests_total{} 1
# HELP elapsed Histogram of elapsed.
# TYPE elapsed histogram
elapsed_sum{} 10.0
elapsed_count{} 1
elapsed_bucket{le="0.0",} 0
elapsed_bucket{le="+Inf",} 1
# EOF
Fix patch with unit test: https://github.com/prometheus/client_rust/compare/master...tylerlevine:client_rust:histogram-empty-family-labels-fix
The idea behind the fix is that the trailing comma behind the additional labels is only added if the encoding of the family labels is non-empty. I'm not very familiar with this library so maybe there's a better approach here.
With this change the metrics output appears as expected, with no extraneous commas in the bucket label lists:
$ curl localhost:8080/handler; curl localhost:8080/metrics
okay# HELP requests Count of requests.
# TYPE requests counter
requests_total{} 1
# HELP elapsed Histogram of elapsed.
# TYPE elapsed histogram
elapsed_sum{} 10.0
elapsed_count{} 1
elapsed_bucket{le="0.0"} 0
elapsed_bucket{le="+Inf"} 1
# EOF
