Have Opentelemetry error handler to use tracing::error (#852)

* Set global opentelemetry error handler to use tracing::error

* Add OTel HTTP support

* Revert "Add OTel HTTP support"

This reverts commit 513c533.

* attempting to write a new test to validate this new setting

* Added test

core/src/telemetry/otel.rs

@@ -12,7 +12,7 @@ use super::{
 };
 use crate::{abstractions::dbg_panic, telemetry::metrics::DEFAULT_S_BUCKETS};
 use opentelemetry::{
-    self,
+    self, global,
     metrics::{Meter, MeterProvider as MeterProviderT},
     Key, KeyValue, Value,
 };
@@ -121,6 +121,9 @@ pub(super) fn augment_meter_provider_with_defaults(
 pub fn build_otlp_metric_exporter(
     opts: OtelCollectorOptions,
 ) -> Result<CoreOtelMeter, anyhow::Error> {
+    global::set_error_handler(|err| {
+        tracing::error!("{}", err);
+    })?;
     let exporter = match opts.protocol {
         OtlpProtocol::Grpc => {
             let mut exporter = opentelemetry_otlp::TonicExporterBuilder::default()

tests/integ_tests/metrics_tests.rs

@@ -1,7 +1,13 @@
 use anyhow::anyhow;
 use assert_matches::assert_matches;
-use std::string::ToString;
-use std::{collections::HashMap, env, net::SocketAddr, sync::Arc, time::Duration};
+use std::{
+    collections::HashMap,
+    env,
+    net::SocketAddr,
+    string::ToString,
+    sync::{Arc, Mutex},
+    time::Duration,
+};
 use temporal_client::{
     WorkflowClientTrait, WorkflowOptions, WorkflowService, REQUEST_LATENCY_HISTOGRAM_NAME,
 };
@@ -48,6 +54,7 @@ use temporal_sdk_core_test_utils::{
     PROMETHEUS_QUERY_API,
 };
 use tokio::{join, sync::Barrier, task::AbortHandle};
+use tracing_subscriber::fmt::MakeWriter;
 use url::Url;
 
 static ANY_PORT: &str = "127.0.0.1:0";
@@ -900,3 +907,69 @@ async fn evict_on_complete_does_not_count_as_forced_eviction() {
     // Metric shouldn't show up at all, since it's zero the whole time.
     assert!(!body.contains("temporal_sticky_cache_total_forced_eviction"));
 }
+
+struct CapturingWriter {
+    buf: Arc<Mutex<Vec<u8>>>,
+}
+
+impl MakeWriter<'_> for CapturingWriter {
+    type Writer = CapturingHandle;
+
+    fn make_writer(&self) -> Self::Writer {
+        CapturingHandle(self.buf.clone())
+    }
+}
+
+struct CapturingHandle(Arc<Mutex<Vec<u8>>>);
+
+impl std::io::Write for CapturingHandle {
+    fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
+        let mut b = self.0.lock().unwrap();
+        b.extend_from_slice(buf);
+        Ok(buf.len())
+    }
+    fn flush(&mut self) -> std::io::Result<()> {
+        Ok(())
+    }
+}
+
+#[tokio::test]
+async fn otel_errors_logged_as_errors() {
+    // Set up tracing subscriber to capture ERROR logs
+    let logs = Arc::new(Mutex::new(Vec::new()));
+    let writer = CapturingWriter { buf: logs.clone() };
+    let subscriber = tracing_subscriber::fmt().with_writer(writer).finish();
+    let _guard = tracing::subscriber::set_default(subscriber);
+
+    let opts = OtelCollectorOptionsBuilder::default()
+        .url("https://localhostt:9995/v1/metrics".parse().unwrap()) // Invalid endpoint
+        .build()
+        .unwrap();
+    let exporter = build_otlp_metric_exporter(opts).unwrap();
+
+    let telemopts = TelemetryOptionsBuilder::default()
+        .metrics(Arc::new(exporter) as Arc<dyn CoreMeter>)
+        .build()
+        .unwrap();
+
+    let rt = CoreRuntime::new_assume_tokio(telemopts).unwrap();
+    let mut starter = CoreWfStarter::new_with_runtime("otel_errors_logged_as_errors", rt);
+    let _worker = starter.get_worker().await;
+
+    // Wait to allow exporter to attempt sending metrics and fail.
+    tokio::time::sleep(Duration::from_secs(2)).await;
+
+    let logs = logs.lock().unwrap();
+    let log_str = String::from_utf8_lossy(&logs);
+
+    assert!(
+        log_str.contains("ERROR"),
+        "Expected ERROR log not found in logs: {}",
+        log_str
+    );
+    assert!(
+        log_str.contains("Metrics exporter otlp failed with the grpc server returns error"),
+        "Expected an OTel exporter error message in logs: {}",
+        log_str
+    );
+}