Fix tracing grpc example (#1493)

Cleaned up readme as we already removed tracing-opentelemetry and jaeger
from it.

examples/README.md

@@ -32,9 +32,10 @@ This example uses following crates from this repo:
 **Tracing**
 
 This example uses following crates from this repo:
+
 - opentelemetry(tracing)
-- opentelemetry-jaeger
+- opentelemetry-stdout
 
 The application is built using `tokio`.
 
-Check this example if you want to understand *how to integrate tracing with opentelemetry*.
+Check this example if you want to understand *how to create spans and propagate/restore context in OpenTelemetry*.

examples/tracing-grpc/Cargo.toml

@@ -20,6 +20,7 @@ opentelemetry-stdout = { path = "../../opentelemetry-stdout", features = ["trace
 prost = { workspace = true }
 tokio = { workspace = true, features = ["full"] }
 tonic = { workspace = true }
+serde_json = { workspace = true }
 
 [build-dependencies]
 tonic-build = "0.9.2"

examples/tracing-grpc/README.md

@@ -1,24 +1,25 @@
 # GRPC example
 
-Example showing [Tonic] client and server interaction with OpenTelemetry context propagation.  [tracing_opentelemetry](https://docs.rs/tracing-opentelemetry/0.4.0/tracing_opentelemetry/) is used to hook into the [tracing](https://github.com/tokio-rs/tracing) ecosystem, which enables drop-in replacements for [log](https://github.com/rust-lang/log) macros and an `#[instrument]` macro that will automatically add spans to your functions.
+Example showing [Tonic] client and server interaction with OpenTelemetry context
+propagation. Traces are exported to stdout.
 
 [Tonic]: https://github.com/hyperium/tonic
 
-Examples
---------
+## Running the example
 
 ```shell
-# Run jaeger in background
-$ docker run -d -p6831:6831/udp -p6832:6832/udp -p16686:16686 jaegertracing/all-in-one:latest
-
-# Run the server
+# Run the server first
 $ cargo run --bin grpc-server
 
 # Now run the client to make a request to the server
 $ cargo run --bin grpc-client
-
-# View spans (see the image below)
-$ firefox http://localhost:16686/
 ```
 
-![Jaeger UI](trace.png)
+Observe that the traces are exported to stdout, and that they share the same
+TraceId. Also, the server span would be parented to the client span. The example
+demonstrates how to propagate and restore OpenTelemetry context when making
+out-of-process calls, so as to ensure the same trace is continued in the next
+process. The client here initiates the trace by creating the root client span,
+and it propagates its context to the server. The server, extracts the context,
+and creates its own server span using the extracted context, ensuring both spans
+are correlated.

examples/tracing-grpc/src/client.rs

@@ -4,7 +4,7 @@ use opentelemetry::{global, propagation::Injector};
 use opentelemetry_sdk::{
     propagation::TraceContextPropagator, runtime::Tokio, trace::TracerProvider,
 };
-use opentelemetry_stdout::SpanExporter;
+use opentelemetry_stdout::SpanExporterBuilder;
 
 use opentelemetry::{
     trace::{SpanKind, TraceContextExt, Tracer},
@@ -15,7 +15,15 @@ fn init_tracer() {
     global::set_text_map_propagator(TraceContextPropagator::new());
     // Install stdout exporter pipeline to be able to retrieve the collected spans.
     let provider = TracerProvider::builder()
-        .with_batch_exporter(SpanExporter::default(), Tokio)
+        .with_batch_exporter(
+            SpanExporterBuilder::default()
+                .with_encoder(|writer, data| {
+                    serde_json::to_writer_pretty(writer, &data).unwrap();
+                    Ok(())
+                })
+                .build(),
+            Tokio,
+        )
         .build();
 
     global::set_tracer_provider(provider);

examples/tracing-grpc/src/server.rs

@@ -8,14 +8,22 @@ use opentelemetry::{
 use opentelemetry_sdk::{
     propagation::TraceContextPropagator, runtime::Tokio, trace::TracerProvider,
 };
-use opentelemetry_stdout::SpanExporter;
+use opentelemetry_stdout::SpanExporterBuilder;
 use tonic::{transport::Server, Request, Response, Status};
 
 fn init_tracer() {
     global::set_text_map_propagator(TraceContextPropagator::new());
     // Install stdout exporter pipeline to be able to retrieve the collected spans.
     let provider = TracerProvider::builder()
-        .with_batch_exporter(SpanExporter::default(), Tokio)
+        .with_batch_exporter(
+            SpanExporterBuilder::default()
+                .with_encoder(|writer, data| {
+                    serde_json::to_writer_pretty(writer, &data).unwrap();
+                    Ok(())
+                })
+                .build(),
+            Tokio,
+        )
         .build();
 
     global::set_tracer_provider(provider);