chore: Add warning on Prometheus crate (#2831)

Author: cijothomas

opentelemetry-otlp/src/lib.rs

@@ -103,7 +103,61 @@
 //! After running your application configured with the OTLP exporter, view traces at:
 //! `http://localhost:16686`
 //!
-//! ## Using with Prometheus (TODO)
+//! ## Using with Prometheus
+//!
+//! Prometheus natively supports accepting metrics via the OTLP protocol
+//! (HTTP/protobuf). You can [run
+//! Prometheus](https://prometheus.io/docs/prometheus/latest/installation/) with
+//! the following command:
+//!
+//! ```shell
+//! docker run -p 9090:9090 -v ./prometheus.yml:/etc/prometheus/prometheus.yml prom/prometheus --config.file=/etc/prometheus/prometheus.yml --web.enable-otlp-receiver
+//! ```
+//!
+//! (An empty prometheus.yml file is sufficient for this example.)
+//!
+//! Modify your application to export metrics via OTLP:
+//!
+//! ```no_run
+//! # #[cfg(all(feature = "metrics", feature = "http-proto"))]
+//! # {
+//! use opentelemetry::global;
+//! use opentelemetry::metrics::Meter;
+//! use opentelemetry::KeyValue;
+//! use opentelemetry_otlp::Protocol;
+//! use opentelemetry_otlp::WithExportConfig;
+//!
+//! fn main() -> Result<(), Box<dyn std::error::Error + Send + Sync + 'static>> {
+//!     // Initialize OTLP exporter using HTTP binary protocol
+//!     let exporter = opentelemetry_otlp::MetricExporter::builder()
+//!         .with_http()
+//!         .with_protocol(Protocol::HttpBinary)
+//!         .with_endpoint("http://localhost:9090/api/v1/otlp/v1/metrics")
+//!         .build()?;
+//!
+//!     // Create a meter provider with the OTLP Metric exporter
+//!     let meter_provider = opentelemetry_sdk::metrics::SdkMeterProvider::builder()
+//!         .with_periodic_exporter(exporter)
+//!         .build();
+//!     global::set_meter_provider(meter_provider.clone());
+//!
+//!     // Get a meter
+//!     let meter = global::meter("my_meter");
+//!
+//!     // Create a metric
+//!     let counter = meter.u64_counter("my_counter").build();
+//!     counter.add(1, &[KeyValue::new("key", "value")]);
+//!
+//!     // Shutdown the meter provider. This will trigger an export of all metrics.
+//!     meter_provider.shutdown()?;
+//!
+//!     Ok(())
+//! # }
+//! }
+//! ```
+//!
+//! After running your application configured with the OTLP exporter, view metrics at:
+//! `http://localhost:9090`
 //! ## Show Logs, Metrics too (TODO)
 //!
 //! ## Performance

opentelemetry-prometheus/README.md

@@ -6,8 +6,19 @@
 
 [`Prometheus`] integration for applications instrumented with [`OpenTelemetry`]. 
 
-**The development of prometheus exporter has halt until the Opentelemetry metrics API and SDK reaches 1.0. Current 
-implementation is based on Opentelemetry API and SDK 0.27**.
+**Warning: This crate is no longer recommended for use.**
+
+Development of the Prometheus exporter has been discontinued. See the related
+[issue](https://github.com/open-telemetry/opentelemetry-rust/issues/2451). This
+crate depends on the unmaintained `protobuf` crate and has unresolved security
+vulnerabilities. Version 0.29 will be the final release.
+
+For Prometheus integration, we strongly recommend using the [OTLP] exporter
+instead. Prometheus [natively supports
+OTLP](https://prometheus.io/docs/guides/opentelemetry/#enable-the-otlp-receiver),
+providing a more stable and actively maintained solution.
+
+[OTLP]: https://docs.rs/opentelemetry-otlp/latest/opentelemetry_otlp/
 
 [![Crates.io: opentelemetry-prometheus](https://img.shields.io/crates/v/opentelemetry-prometheus.svg)](https://crates.io/crates/opentelemetry-prometheus)
 [![Documentation](https://docs.rs/opentelemetry-prometheus/badge.svg)](https://docs.rs/opentelemetry-prometheus)

opentelemetry-prometheus/src/lib.rs

@@ -1,9 +1,19 @@
 //! An OpenTelemetry exporter for [Prometheus] metrics.
 //!
-//! <div class="warning"> The development of prometheus exporter has halt until the Opentelemetry metrics API and SDK reaches 1.0. Current
-//! implementation is based on Opentelemetry API and SDK 0.23.</div>
+//! <div class="warning">
+//! <strong>Warning: This crate is no longer recommended for use.</strong><br><br>
+//! Development of the Prometheus exporter has been discontinued. See the related 
+//! [issue](https://github.com/open-telemetry/opentelemetry-rust/issues/2451).
+//! This crate depends on the unmaintained `protobuf` crate and has unresolved 
+//! security vulnerabilities. Version 0.29 will be the final release.
+//!
+//! For Prometheus integration, we strongly recommend using the [OTLP] exporter instead.
+//! Prometheus [natively supports OTLP](https://prometheus.io/docs/guides/opentelemetry/#enable-the-otlp-receiver),
+//! providing a more stable and actively maintained solution.
+//! </div>
 //!
 //! [Prometheus]: https://prometheus.io
+//! [OTLP]: https://docs.rs/opentelemetry-otlp/latest/opentelemetry_otlp/
 //!
 //! ```
 //! use opentelemetry::{metrics::MeterProvider, KeyValue};