chore: improve comments and simplify a bit

src/commands/metrics.rs

@@ -1,24 +1,59 @@
+use super::run::Config;
 use parking_lot::{const_rwlock, RwLock};
 use tracing_deps::{
-    opentelemetry::{sdk::Resource, KeyValue},
     opentelemetry_prometheus,
     prometheus::{Encoder, TextEncoder},
 };
 
+// TODO(jacobmarble): better way to write-once-read-many without a lock
+// TODO(jacobmarble): generic OTel exporter, rather than just prometheus
 static PROMETHEUS_EXPORTER: RwLock<Option<opentelemetry_prometheus::PrometheusExporter>> =
     const_rwlock(None);
 
-pub fn init_metrics() {
-    let exporter = opentelemetry_prometheus::exporter()
-        .with_resource(Resource::new(vec![KeyValue::new(
-            "service.name",
-            "influxdb-iox",
-        )]))
-        .init();
+/// Initializes metrics.
+///
+/// # Example
+///
+/// ```
+/// let meter = opentelemetry::global::meter("iox");
+/// let counter = meter
+///     .u64_counter("a.counter")
+///     .with_description("Counts things")
+///     .init();
+/// let recorder = meter
+///     .i64_value_recorder("a.value_recorder")
+///     .with_description("Records values")
+///     .init();
+///
+/// counter.add(100, &[KeyValue::new("key", "value")]);
+/// recorder.record(100, &[KeyValue::new("key", "value")]);
+/// ```
+pub fn init_metrics(_config: &Config) {
+    // TODO add flags to config, to configure the OpenTelemetry exporter (OTLP)
+    // This sets the global meter provider, for other code to use
+    let exporter = opentelemetry_prometheus::exporter().init();
     let mut guard = PROMETHEUS_EXPORTER.write();
     *guard = Some(exporter);
 }
 
+/// Gets current metrics state, in UTF-8 encoded Prometheus Exposition Format.
+/// https://prometheus.io/docs/instrumenting/exposition_formats/
+///
+/// # Example
+///
+/// ```
+/// # HELP a_counter Counts things
+/// # TYPE a_counter counter
+/// a_counter{key="value"} 100
+/// # HELP a_value_recorder Records values
+/// # TYPE a_value_recorder histogram
+/// a_value_recorder_bucket{key="value",le="0.5"} 0
+/// a_value_recorder_bucket{key="value",le="0.9"} 0
+/// a_value_recorder_bucket{key="value",le="0.99"} 0
+/// a_value_recorder_bucket{key="value",le="+Inf"} 1
+/// a_value_recorder_sum{key="value"} 100
+/// a_value_recorder_count{key="value"} 1
+/// ```
 pub fn metrics_as_text() -> Vec<u8> {
     let metric_families = PROMETHEUS_EXPORTER
         .read()

src/influxdb_ioxd.rs

@@ -102,7 +102,7 @@ pub async fn main(logging_level: LoggingLevel, config: Config) -> Result<()> {
     let logging_level = logging_level.combine(LoggingLevel::new(config.verbose_count));
 
     let _drop_handle = logging_level.setup_logging(&config);
-    let _metrics_guard = metrics::init_metrics();
+    metrics::init_metrics(&config);
 
     // Install custom panic handler and forget about it.
     //