OpenTelemetry Metrics Demo

A Go application demonstrating OpenTelemetry metrics (Counter, Histogram, Gauge) integrated with SigNoz Cloud. This simple e-commerce cart API tracks HTTP errors, request latency, and cart item counts.

What This Project Demonstrates

• Counter Metric: Tracking HTTP error counts (4xx/5xx responses)
• Histogram Metric: Measuring request latency distribution
• Gauge Metric: Monitoring current cart item totals using observable callbacks

Prerequisites

• Go 1.21 or higher
• SigNoz Cloud account (Sign up here)

Quick Start

1. Clone the Repository

git clone https://github.com/shreyanshjain7174/otel-metrics-demo.git
cd otel-metrics-demo

2. Install Dependencies

go mod download

3. Configure Environment Variables

Copy the example environment file and fill in your SigNoz credentials:

cp .env.example .env

Edit .env with your SigNoz Cloud details:

OTEL_EXPORTER_OTLP_ENDPOINT=ingest.us.signoz.cloud:443
OTEL_EXPORTER_OTLP_HEADERS=signoz-access-token=<your-token>
SERVICE_NAME=otel-metrics-demo
SERVER_PORT=8080

Then load the environment variables:

source .env
# Or export them individually
export OTEL_EXPORTER_OTLP_ENDPOINT="ingest.us.signoz.cloud:443"
export OTEL_EXPORTER_OTLP_HEADERS="signoz-access-token=<your-token>"

4. Run the Application

go run main.go

Or build and run:

go build -o otel-metrics-demo
./otel-metrics-demo

You should see output like:

level=INFO msg="Configuration loaded" endpoint=ingest.us.signoz.cloud:443 service=otel-metrics-demo port=8080
level=INFO msg="Initializing OpenTelemetry" ...
level=INFO msg="OpenTelemetry initialized successfully"
level=INFO msg="Starting server" port=8080

Environment Variables

Variable	Description	Default
OTEL_EXPORTER_OTLP_ENDPOINT	SigNoz Cloud OTLP endpoint	(required)
OTEL_EXPORTER_OTLP_HEADERS	Authentication header with token	(required)
SERVICE_NAME	Service name in SigNoz	otel-metrics-demo
SERVER_PORT	HTTP server port	8080

API Endpoints

Method	Endpoint	Description	Request Body
POST	/cart/:userId/add	Add item to cart	{"item": "name", "quantity": 1}
DELETE	/cart/:userId/remove	Remove item from cart	{"item": "name"}
GET	/cart/:userId	Get cart details	-
GET	/error	Trigger 500 error (testing)	-
GET	/health	Health check	-

Testing the API

Add items to cart

curl -X POST http://localhost:8080/cart/user1/add \
  -H "Content-Type: application/json" \
  -d '{"item":"laptop","quantity":1}'

Get cart

curl http://localhost:8080/cart/user1

Remove item

curl -X DELETE http://localhost:8080/cart/user1/remove \
  -H "Content-Type: application/json" \
  -d '{"item":"laptop"}'

Trigger error (for testing error counter)

curl http://localhost:8080/error

Generate Load for Testing

Use this script to generate traffic and see metrics in SigNoz:

#!/bin/bash
for i in {1..100}; do
    curl -s -X POST http://localhost:8080/cart/user$((i%10))/add \
      -H "Content-Type: application/json" \
      -d "{\"item\":\"item$i\",\"quantity\":$((i%5+1))}" > /dev/null

    # Occasionally trigger errors
    if [ $((i % 10)) -eq 0 ]; then
        curl -s http://localhost:8080/error > /dev/null
    fi

    sleep 0.1
done
echo "Load test complete!"

Metrics Exported

Metric Name	Type	Description
http.server.errors	Counter	Total HTTP error responses (4xx/5xx)
http.server.duration	Histogram	Request latency in milliseconds
cart.items.total	Gauge	Current total items across all carts

Viewing Metrics in SigNoz

1. Log in to your SigNoz Cloud account
2. Navigate to Metrics → Metrics Explorer
3. Search for your metrics:
   • http_server_errors (Counter)
   • http_server_duration (Histogram)
   • cart_items_total (Gauge)
4. Use aggregations like Sum, Rate, P50, P95, P99

Project Structure

.
├── main.go              # Application entry point
├── config/
│   └── config.go        # Configuration management
├── handlers/
│   └── cart.go          # HTTP endpoint handlers
├── middleware/
│   └── metrics.go       # Metrics collection middleware
├── metrics/
│   └── otel.go          # OpenTelemetry initialization
├── models/
│   └── cart.go          # Request/response models
├── storage/
│   └── memory.go        # In-memory cart storage
├── .env.example         # Environment variables template
├── go.mod
└── go.sum

Troubleshooting

Metrics not appearing in SigNoz

1. Verify environment variables are set correctly
2. Check the OTLP endpoint format: ingest.<region>.signoz.cloud:443
3. Ensure your access token is valid
4. Wait 10-30 seconds (metrics export every 10s)
5. Check application logs for connection errors

Debug logging

Modify the logger level in main.go:

logger := slog.New(slog.NewTextHandler(os.Stdout, &slog.HandlerOptions{
    Level: slog.LevelDebug,
}))

Learn More

• OpenTelemetry Go Documentation
• SigNoz Documentation
• Full Tutorial: Beginner's Guide

License

MIT