Document Getting Started with Prometheus and Grafana (#1396)

Co-authored-by: Lalit Kumar Bhasin <lalit_fin@yahoo.com>

examples/prometheus/README.md

@@ -0,0 +1,208 @@
+# Getting Started with Prometheus and Grafana
+
+- [Export metrics from the application](#export-metrics-from-the-application)
+  - [Check results in the browser](#check-results-in-the-browser)
+- [Collect metrics using Prometheus](#collect-metrics-using-prometheus)
+  - [Configuration](#configuration)
+  - [Start Prometheus](#start-prometheus)
+  - [View results in Prometheus](#view-results-in-prometheus)
+- [Explore metrics using Grafana](#explore-metrics-using-grafana)
+- [Learn more](#learn-more)
+
+## Export metrics from the application
+
+It is highly recommended to go over the [ostream-metrics](../metrics_simple/README.md)
+doc before following along this document.
+
+Run the application with:
+
+```sh
+bazel run //examples/prometheus:prometheus_example
+```
+
+The main difference between the [ostream-metrics](../metrics_simple/README.md)
+example with this one is that the line below is replaced:
+
+```cpp
+std::unique_ptr<metric_sdk::MetricExporter> exporter{
+    new exportermetrics::OStreamMetricExporter};
+
+```
+
+with
+
+```cpp
+std::unique_ptr<metrics_sdk::MetricExporter> exporter{
+    new metrics_exporter::PrometheusExporter(opts)};
+```
+
+OpenTelemetry `PrometheusExporter` will export
+data via the endpoint defined by
+`metrics_exporter::PrometheusExporterOptions::url`,
+which is `http://localhost:9464/` by default.
+
+```mermaid
+graph LR
+
+subgraph SDK
+  MeterProvider
+  MetricReader[PeriodicExportingMetricReader]
+  PrometheusExporter["PrometheusExporter<br/>(http://localhost:9464/)"]
+end
+
+subgraph API
+  Instrument["Meter(#quot;prometheus_metric_example#quot;, #quot;1.0#quot;)<br/>Histogram(#quot;prometheus_metric_example_histogram#quot;)"]
+end
+
+Instrument --> | Measurements | MeterProvider
+
+MeterProvider --> | Metrics | MetricReader --> | Pull | PrometheusExporter
+```
+
+Also, for our learning purpose, we use a while-loop to keep recoring random
+values until the program stops.
+
+```cpp
+while (true)
+{
+    double val = (rand() % 700) + 1.1;
+    std::map<std::string, std::string> labels = get_random_attr();
+    auto labelkv = opentelemetry::common::KeyValueIterableView<decltype(labels)>{labels};
+    histogram_counter->Record(val, labelkv, context);
+    std::this_thread::sleep_for(std::chrono::milliseconds(50));
+}
+```
+
+### Check results in the browser
+
+Start the application and keep it running. Now we should be able to see the
+metrics at [http://localhost:9464/metrics](http://localhost:9464/metrics) from a
+web browser:
+
+![Browser UI](https://user-images.githubusercontent.com/71217171/168492500-12bd1c99-33ab-4515-a294-17bc349b5d13.png)
+
+Now, we understand how we can configure `PrometheusExporter` to export metrics.
+Next, we are going to learn about how to use Prometheus to collect the metrics.
+
+## Collect metrics using Prometheus
+
+Follow the [first steps](https://prometheus.io/docs/introduction/first_steps/)
+to download the [latest release](https://prometheus.io/download/) of Prometheus.
+It is also possible to use `prom/prometheus` docker image.
+
+### Configuration
+
+After downloading, extract it to a local location that's easy to
+access. We will find the default Prometheus configuration YAML file in the
+folder, named `prometheus.yml`.
+
+```yaml
+global:
+  scrape_interval: 5s
+  scrape_timeout: 2s
+  evaluation_interval: 5s
+alerting:
+  alertmanagers:
+  - follow_redirects: true
+    scheme: http
+    timeout: 5s
+    api_version: v2
+    static_configs:
+    - targets: [localhost:9464]
+scrape_configs:
+  - job_name: otel
+    static_configs:
+      - targets: ['localhost:9464']
+```
+
+### Start Prometheus
+
+Follow the instructions from
+[starting-prometheus](https://prometheus.io/docs/introduction/first_steps/#starting-prometheus)
+to start the Prometheus server and verify it has been started successfully.
+
+Please note that we will need pass in `prometheus.yml` file as the argument
+or mount as volume:
+
+```console
+./prometheus --config.file=prometheus.yml
+# OR:
+docker run -p 9090:9090 -v $(pwd):/etc/prometheus --network="host" prom/prometheus
+```
+
+### View results in Prometheus
+
+To use the graphical interface for viewing our metrics with Prometheus, navigate
+to [http://localhost:9090/graph](http://localhost:9090/graph),
+and type `prometheus_metric_example_bucket` in the expression bar of the UI;
+finally, click the execute button.
+
+We should be able to see the following chart from the browser:
+
+![Prometheus UI](https://user-images.githubusercontent.com/71217171/168492437-f9769db1-6f9e-49c6-8ef0-85f5e1188ba0.png)
+
+From the legend, we can see that the `instance` name and the `job` name are the
+values we have set in `prometheus.yml`.
+
+Congratulations!
+
+Now we know how to configure Prometheus server and deploy OpenTelemetry
+`PrometheusExporter` to export our metrics. Next, we are going to explore a tool
+called Grafana, which has powerful visualizations for the metrics.
+
+## Explore metrics using Grafana
+
+[Install Grafana](https://grafana.com/docs/grafana/latest/installation/).
+
+Start the standalone Grafana server (`grafana-server.exe` or
+`./bin/grafana-server`, depending on the operating system). Then, use the
+browser to navigate to [http://localhost:3000/](http://localhost:3000/).
+It is also possible to run `grafana/grafana` container:
+
+```sh
+docker run -d -p 3000:3000 --network="host" grafana/grafana
+```
+
+Follow the instructions in the Grafana getting started
+[doc](https://grafana.com/docs/grafana/latest/getting-started/getting-started/#step-2-log-in)
+to log in.
+
+After successfully logging in, click on the Configuration icon
+on the panel at the left hand side, and click on Prometheus.
+Type in the default endpoint of Prometheus as suggested by the UI
+as the value for the URI.
+
+```console
+http://localhost:9090
+```
+
+Then, click on the Explore icon on the left panel of
+the website - we should be able to write some queries to explore our metrics
+now!
+
+Feel free to find some handy PromQL
+[here](https://promlabs.com/promql-cheat-sheet/).
+
+![Grafana
+UI](https://user-images.githubusercontent.com/71217171/168492482-047a4429-4854-4b3c-a2dd-4d75362090d5.png)
+
+```mermaid
+graph TD
+
+subgraph Prometheus
+  PrometheusScraper
+  PrometheusDatabase
+end
+
+PrometheusExporter["PrometheusExporter<br/>(listening at #quot;http://localhost:9464/#quot;)"] -->|HTTP GET| PrometheusScraper{{"Prometheus scraper<br/>(polling #quot;http://localhost:9464/metrics#quot; every 5 seconds)"}}
+PrometheusScraper --> PrometheusDatabase[("Prometheus TSDB (time series database)")]
+PrometheusDatabase -->|http://localhost:9090/graph| PrometheusUI["Browser<br/>(Prometheus Dashboard)"]
+PrometheusDatabase -->|http://localhost:9090/api/| Grafana[Grafana Server]
+Grafana -->|http://localhost:3000/dashboard| GrafanaUI["Browser<br/>(Grafana Dashboard)"]
+```
+
+## Learn more
+
+- [What is Prometheus?](https://prometheus.io/docs/introduction/overview/)
+- [Grafana support for
+  Prometheus](https://prometheus.io/docs/visualization/grafana/#creating-a-prometheus-graph)

examples/prometheus/prometheus.yml

@@ -9,8 +9,8 @@ alerting:
     timeout: 5s
     api_version: v2
     static_configs:
-    - targets: [localhost:8080]
+    - targets: [localhost:9464]
 scrape_configs:
   - job_name: otel
     static_configs:
-      - targets: ['localhost:8080']
+      - targets: ['localhost:9464']

exporters/prometheus/include/opentelemetry/exporters/prometheus/exporter.h

@@ -28,10 +28,10 @@ namespace exporter
 namespace metrics
 {
 
-inline const std::string GetOtlpDefaultHttpEndpoint()
+inline const std::string GetPrometheusDefaultHttpEndpoint()
 {
   constexpr char kPrometheusEndpointEnv[]     = "PROMETHEUS_EXPORTER_ENDPOINT";
-  constexpr char kPrometheusEndpointDefault[] = "localhost:8080";
+  constexpr char kPrometheusEndpointDefault[] = "localhost:9464";
 
   auto endpoint = opentelemetry::sdk::common::GetEnvironmentVariable(kPrometheusEndpointEnv);
   return endpoint.size() ? endpoint : kPrometheusEndpointDefault;
@@ -43,7 +43,7 @@ inline const std::string GetOtlpDefaultHttpEndpoint()
 struct PrometheusExporterOptions
 {
   // The endpoint the Prometheus backend can collect metrics from
-  std::string url = GetOtlpDefaultHttpEndpoint();
+  std::string url = GetPrometheusDefaultHttpEndpoint();
 };
 
 class PrometheusExporter : public sdk::metrics::MetricExporter