docs: add observability setup instructions

Author: xBlaz3kx

docs/observability.md

@@ -0,0 +1,69 @@
+# Observability in ocpp-go
+
+## Metrics
+
+The library currently supports only websocket and ocpp-j server metrics, which are exported via OpenTelemetry.
+To enable metrics, you need to set the metrics exporter on the server:
+
+```go
+// sets up OTLP metrics exporter
+func setupMetrics(address string) error {
+grpcOpts := []grpc.DialOption{
+grpc.WithTransportCredentials(insecure.NewCredentials()),
+}
+
+client, err := grpc.NewClient(address, grpcOpts...)
+
+if err != nil {
+return errors.Wrap(err, "failed to create gRPC connection to collector")
+}
+
+ctx := context.Background()
+
+exporter, err := otlpmetricgrpc.New(ctx, otlpmetricgrpc.WithGRPCConn(client))
+if err != nil {
+return errors.Wrap(err, "failed to create otlp metric exporter")
+}
+
+resource, err := resource.New(ctx,
+resource.WithAttributes(
+semconv.ServiceNameKey.String("centralSystem-demo"),
+semconv.ServiceVersionKey.String("example"),
+),
+resource.WithFromEnv(),
+resource.WithContainer(),
+resource.WithOS(),
+resource.WithOSType(),
+resource.WithHost(),
+)
+if err != nil {
+return errors.Wrap(err, "failed to create resource")
+}
+
+meterProvider := metricsdk.NewMeterProvider(
+metricsdk.WithReader(
+metricsdk.NewPeriodicReader(
+exporter,
+metricsdk.WithInterval(10*time.Second),
+),
+),
+metricsdk.WithResource(resource),
+)
+
+otel.SetMeterProvider(meterProvider)
+return nil
+}
+```
+
+You can check out the [reference implementation](../example/1.6/cs/central_system_sim.go), and deploy it with:
+
+```bash
+make example-ocpp16-observability
+```
+
+> Note: Deploying the example requires docker and docker compose to be installed.
+
+The deployment will start a central system with metrics enabled and a
+full [observability stack](https://github.com/grafana/docker-otel-lgtm).
+
+You can log in to Grafana at http://localhost:3000 with the credentials `admin/admin`.