few comments on otlp

docs/migration_0.28.md

@@ -65,6 +65,9 @@ Please note the following:
    `opentelemetry-otlp`. grpc-tonic, reqwest-blocking-client In other words,
    `reqwest` and `hyper` are not supported. If using `grpc-tonic`, the OTLP
    Exporter must be created from within a Tokio runtime.
+   If using exporters other than `opentelemetry-otlp`, consult the docs
+   for the same to know if there are any restrictions/requirements on async
+   runtime.
 2. Timeout enforcement is now moved to Exporters. i.e
 BatchProcessor,PeriodicReader does not enforce timeouts. For logs and traces,
 `max_export_timeout` (on Processors) or `OTEL_BLRP_EXPORT_TIMEOUT` or
@@ -134,7 +137,6 @@ fed back to OTel, creating an infinite loop. This can be achieved via proper
 filtering. The OTLP Examples in the repo shows how to achieve this. It also
 shows how to send OTel's internal logs to stdtout using `tracing::Fmt`.
 
-
 ## Full example
 
 A fully runnable example application using OTLP Exporter is provided in this
@@ -144,7 +146,8 @@ the changes required to be made.
 [Basic OTLP Example
 (0.27)](https://github.com/open-telemetry/opentelemetry-rust/tree/opentelemetry-otlp-0.27.0/opentelemetry-otlp/examples)
 [Basic OTLP Example
-(0.28)](https://github.com/open-telemetry/opentelemetry-rust/tree/opentelemetry-otlp-0.28.0/opentelemetry-otlp/examples)
+(0.28)](https://github.com/open-telemetry/opentelemetry-rust/tree/opentelemetry-otlp-0.27.0/opentelemetry-otlp/examples)
+// TODO: Update this link after github tag is created.
 
 This guide covers only the most common breaking changes. If you’re using custom
 exporters or processors (or authoring one), please consult the changelog for

opentelemetry-otlp/examples/basic-otlp-http/src/main.rs

@@ -1,4 +1,3 @@
-/// To use hyper as the HTTP client - cargo run --features="hyper" --no-default-features
 use once_cell::sync::Lazy;
 use opentelemetry::{
     global,
@@ -19,7 +18,7 @@ use tracing_subscriber::EnvFilter;
 
 static RESOURCE: Lazy<Resource> = Lazy::new(|| {
     Resource::builder()
-        .with_service_name("basic-otlp-example")
+        .with_service_name("basic-otlp-example-http")
         .build()
 });
 
@@ -102,10 +101,25 @@ async fn main() -> Result<(), Box<dyn Error + Send + Sync + 'static>> {
         .with(fmt_layer)
         .init();
 
+    // At this point Logs (OTel Logs and Fmt Logs) are initialized, which will
+    // allow internal-logs from Tracing/Metrics initializer to be captured.
+
     let tracer_provider = init_traces();
+    // Set the global tracer provider using a clone of the tracer_provider.
+    // Setting global tracer provider is required if other parts of the application
+    // uses global::tracer() or global::tracer_with_version() to get a tracer.
+    // Cloning simply creates a new reference to the same tracer provider. It is
+    // important to hold on to the tracer_provider here, so as to invoke
+    // shutdown on it when application ends.
     global::set_tracer_provider(tracer_provider.clone());
 
     let meter_provider = init_metrics();
+    // Set the global meter provider using a clone of the meter_provider.
+    // Setting global meter provider is required if other parts of the application
+    // uses global::meter() or global::meter_with_version() to get a meter.
+    // Cloning simply creates a new reference to the same meter provider. It is
+    // important to hold on to the meter_provider here, so as to invoke
+    // shutdown on it when application ends.
     global::set_meter_provider(meter_provider.clone());
 
     let common_scope_attributes = vec![KeyValue::new("scope-key", "scope-value")];
@@ -147,8 +161,8 @@ async fn main() -> Result<(), Box<dyn Error + Send + Sync + 'static>> {
     info!(target: "my-target", "hello from {}. My price is {}", "apple", 1.99);
 
     tracer_provider.shutdown()?;
-    logger_provider.shutdown()?;
     meter_provider.shutdown()?;
+    logger_provider.shutdown()?;
 
     Ok(())
 }

opentelemetry-otlp/examples/basic-otlp/src/main.rs

@@ -15,7 +15,7 @@ use tracing_subscriber::EnvFilter;
 
 static RESOURCE: Lazy<Resource> = Lazy::new(|| {
     Resource::builder()
-        .with_service_name("basic-otlp-example")
+        .with_service_name("basic-otlp-example-grpc")
         .build()
 });
 
@@ -94,10 +94,25 @@ async fn main() -> Result<(), Box<dyn Error + Send + Sync + 'static>> {
         .with(fmt_layer)
         .init();
 
+    // At this point Logs (OTel Logs and Fmt Logs) are initialized, which will
+    // allow internal-logs from Tracing/Metrics initializer to be captured.
+
     let tracer_provider = init_traces();
+    // Set the global tracer provider using a clone of the tracer_provider.
+    // Setting global tracer provider is required if other parts of the application
+    // uses global::tracer() or global::tracer_with_version() to get a tracer.
+    // Cloning simply creates a new reference to the same tracer provider. It is
+    // important to hold on to the tracer_provider here, so as to invoke
+    // shutdown on it when application ends.
     global::set_tracer_provider(tracer_provider.clone());
 
     let meter_provider = init_metrics();
+    // Set the global meter provider using a clone of the meter_provider.
+    // Setting global meter provider is required if other parts of the application
+    // uses global::meter() or global::meter_with_version() to get a meter.
+    // Cloning simply creates a new reference to the same meter provider. It is
+    // important to hold on to the meter_provider here, so as to invoke
+    // shutdown on it when application ends.    
     global::set_meter_provider(meter_provider.clone());
 
     let common_scope_attributes = vec![KeyValue::new("scope-key", "scope-value")];