feat: add methodfrom_env to promethes exporter builder

Fixes #293

Allows configuring the `PrometheusExporter` using environment variables defined in the semantic conventions of the Otel specification. Currently, supports setting the host and port for prometheus in the builder and will fall back to the defaults defined in the otel specification.

opentelemetry-prometheus/CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changelog
 
+## v0.9.0
+
+### Added
+
+- Add `from_env` method to prometheus exporter based on semantic environment vars
+
 ## v0.8.0
 
 ### Changed
@@ -15,9 +21,11 @@
 ## v0.6.0
 
 ### Added
+
 - Add sanitization of prometheus label names #462
 
 ### Changed
+
 - Update to opentelemetry v0.13.0
 - Update prometheus dependency #485
 

opentelemetry-prometheus/src/lib.rs

@@ -80,6 +80,7 @@ use opentelemetry::{
     metrics::{registry::RegistryMeterProvider, MetricsError, NumberKind},
     Key, Value,
 };
+use std::env;
 use std::sync::{Arc, Mutex};
 use std::time::Duration;
 
@@ -122,9 +123,42 @@ pub struct ExporterBuilder {
     ///
     /// If not set a new empty `Registry` is created.
     registry: Option<prometheus::Registry>,
+
+    /// The host used by the prometheus exporter
+    ///
+    /// If not set it will be defaulted to all addresses "0.0.0.0"
+    host: Option<String>,
+
+    /// The port used by the prometheus exporter
+    ///
+    /// If not set it will be defaulted to port "9464"
+    port: Option<String>,
 }
 
 impl ExporterBuilder {
+    /// Set builder fields for host and port from the OS environment variables
+    ///
+    /// Fields set by developer takes precedent and the OS environment variables will be ignored
+    pub fn from_env() -> Self {
+        let mut builder = ExporterBuilder::default();
+
+        if let Some(host) = env::var("OTEL_EXPORTER_PROMETHEUS_HOST")
+            .ok()
+            .filter(|s| !s.is_empty())
+        {
+            builder = builder.with_host(host)
+        }
+
+        if let Some(port) = env::var("OTEL_EXPORTER_PROMETHEUS_PORT")
+            .ok()
+            .filter(|s| !s.is_empty())
+        {
+            builder = builder.with_port(port);
+        }
+
+        builder
+    }
+
     /// Set the resource to be associated with all `Meter`s for this exporter
     pub fn with_resource(self, resource: Resource) -> Self {
         ExporterBuilder {
@@ -160,6 +194,22 @@ impl ExporterBuilder {
         }
     }
 
+    /// Set the host for the prometheus exporter
+    pub fn with_host(self, host: String) -> Self {
+        ExporterBuilder {
+            host: Some(host),
+            ..self
+        }
+    }
+
+    /// Set the port for the prometheus exporter
+    pub fn with_port(self, port: String) -> Self {
+        ExporterBuilder {
+            port: Some(port),
+            ..self
+        }
+    }
+
     /// Set the prometheus registry to be used by this exporter
     pub fn with_registry(self, registry: prometheus::Registry) -> Self {
         ExporterBuilder {
@@ -189,11 +239,16 @@ impl ExporterBuilder {
 
         global::set_meter_provider(controller.provider());
 
+        let host = self.host.unwrap_or_else(|| "0.0.0.0".to_string());
+        let port = self.port.unwrap_or_else(|| "9464".to_string());
+
         PrometheusExporter::new(
             registry,
             controller,
             default_summary_quantiles,
             default_histogram_boundaries,
+            host,
+            port,
         )
     }
 
@@ -218,6 +273,8 @@ pub struct PrometheusExporter {
     controller: Arc<Mutex<PullController>>,
     default_summary_quantiles: Vec<f64>,
     default_histogram_boundaries: Vec<f64>,
+    host: String,
+    port: String,
 }
 
 impl PrometheusExporter {
@@ -227,6 +284,8 @@ impl PrometheusExporter {
         controller: PullController,
         default_summary_quantiles: Vec<f64>,
         default_histogram_boundaries: Vec<f64>,
+        host: String,
+        port: String,
     ) -> Result<Self, MetricsError> {
         let controller = Arc::new(Mutex::new(controller));
         let collector = Collector::with_controller(controller.clone());
@@ -239,6 +298,8 @@ impl PrometheusExporter {
             controller,
             default_summary_quantiles,
             default_histogram_boundaries,
+            host,
+            port,
         })
     }
 
@@ -254,6 +315,16 @@ impl PrometheusExporter {
             .map_err(Into::into)
             .map(|locked| locked.provider())
     }
+
+    /// Get the exporters host for prometheus.
+    pub fn host(&self) -> &str {
+        self.host.as_str()
+    }
+
+    /// Get the exporters port for prometheus.
+    pub fn port(&self) -> &str {
+        self.port.as_str()
+    }
 }
 
 #[derive(Debug)]

opentelemetry-prometheus/tests/integration_test.rs

@@ -1,3 +1,5 @@
+use std::env;
+
 use opentelemetry::sdk::Resource;
 use opentelemetry::{
     metrics::{BatchObserverResult, MeterProvider, ObserverResult},
@@ -159,3 +161,31 @@ fn compare_export(exporter: &PrometheusExporter, mut expected: Vec<&'static str>
 
     assert_eq!(expected.join("\n"), metrics_only.join("\n"))
 }
+
+#[test]
+fn test_from_env() {
+    let otel_exporter_prometheus_host = "OTEL_EXPORTER_PROMETHEUS_HOST";
+    let otel_exporter_prometheus_port = "OTEL_EXPORTER_PROMETHEUS_PORT";
+
+    // environment variables do not exist
+    env::remove_var(otel_exporter_prometheus_host);
+    env::remove_var(otel_exporter_prometheus_port);
+    let exporter = opentelemetry_prometheus::ExporterBuilder::from_env().init();
+    assert_eq!(exporter.host(), "0.0.0.0");
+    assert_eq!(exporter.port(), "9464");
+
+    // environment variables are available and non-empty strings
+    env::set_var(otel_exporter_prometheus_host, "prometheus-test");
+    env::set_var(otel_exporter_prometheus_port, "9000");
+
+    let exporter = opentelemetry_prometheus::ExporterBuilder::from_env().init();
+    assert_eq!(exporter.host(), "prometheus-test");
+    assert_eq!(exporter.port(), "9000");
+
+    // environment variables are available and empty
+    env::set_var(otel_exporter_prometheus_host, "");
+    env::set_var(otel_exporter_prometheus_port, "");
+    let exporter = opentelemetry_prometheus::ExporterBuilder::from_env().init();
+    assert_eq!(exporter.host(), "0.0.0.0");
+    assert_eq!(exporter.port(), "9464");
+}