Add Opentelemetry guide

_vale/config/vocabularies/Docker/accept.txt

@@ -38,6 +38,7 @@ deprovisioning
 deserialization
 deserialize
 Dev
+Dex
 Dev Environments?
 Dex
 displayName

content/guides/opentelemetry.md

@@ -0,0 +1,200 @@
+---
+title: Instrumenting a JavaScript App with OpenTelemetry
+description: &desc Learn how to instrument a JavaScript application using OpenTelemetry in a Dockerized environment.
+keywords: OpenTelemetry, observability, tracing
+linktitle: Instrumenting JS Apps with OpenTelemetry
+summary: *desc
+tags: [app-dev, observability]
+languages: [js]
+params:
+  time: 10 minutes
+---
+
+OpenTelemetry (OTEL) is an open-source observability framework that provides a set of APIs, SDKs, and tools for collecting telemetry data, such as metrics, logs, and traces, from applications. With OpenTelemetry, developers can obtain valuable insights into how their services perform in production or during local development.
+
+A key component of OpenTelemetry is the OpenTelemetry Protocol (OTLP) a general-purpose, vendor-agnostic protocol designed to transmit telemetry data efficiently and reliably. OTLP supports multiple data types (traces, metrics, logs) over HTTP or gRPC, making it the default and recommended protocol for communication between instrumented applications, the OpenTelemetry Collector, and backends such as Jaeger or Prometheus.
+
+This guide walks you through how to instrument a simple Node.js application with OpenTelemetry and run both the app and a collector using Docker. This setup is ideal for local development and testing observability before integrating with external observability platforms like Prometheus, Jaeger, or Grafana.
+
+In this guide, you'll learn how to:
+
+- How to set up OpenTelemetry in a Node.js app.
+- How to run an OpenTelemetry Collector in Docker.
+- How to visualize traces with Jaeger.
+- How to use Docker Compose to manage the full observability stack.
+
+## Using OpenTelemetry with Docker
+
+the official [docker image for opentelemetry](https://hub.docker.com/r/otel/opentelemetry-collector-contrib) provides a convenient way to deploy and manage dex instances. Opentelemetry is available for various cpu architectures, including amd64, armv7, and arm64, ensuring compatibility with different devices and platforms. Same for the [Jaeger docekr image](https://hub.docker.com/r/jaegertracing/jaeger).
+
+## Prerequisites
+
+[Docker Compose](/compose/): Recommended for managing multi-container Docker applications.
+
+Basic knowledge of Node.js and Docker.
+
+## Project Structure
+
+Create the project directory:
+```bash
+mkdir otel-js-app
+cd otel-js-app
+```
+
+```bash
+otel-js-app/
+├── docker-compose.yaml
+├── collector-config.yaml
+├── app/
+│   ├── package.json
+│   ├── app.js
+│   └── tracer.js
+```
+
+## Create a Simple Node.js App
+
+Initialize a basic Node.js app:
+
+```bash
+mkdir app && cd app
+npm init -y
+npm install express @opentelemetry/api @opentelemetry/sdk-node \
+            @opentelemetry/auto-instrumentations-node \
+            @opentelemetry/exporter-trace-otlp-http
+```
+
+Now, add the application logic:
+
+```js
+// app/app.js
+const express = require('express');
+require('./tracer'); // Initialize OpenTelemetry
+
+const app = express();
+
+app.get('/', (req, res) => {
+  res.send('Hello from OpenTelemetry demo app!');
+});
+
+const PORT = 3000;
+app.listen(PORT, () => {
+  console.log(`App listening at http://localhost:${PORT}`);
+});
+```
+
+## Configure OpenTelemetry Tracing
+
+Create the tracer configuration file:
+
+```js
+// app/tracer.js
+const { NodeSDK } = require('@opentelemetry/sdk-node');
+const { getNodeAutoInstrumentations } = require('@opentelemetry/auto-instrumentations-node');
+const { OTLPTraceExporter } = require('@opentelemetry/exporter-trace-otlp-http');
+
+const sdk = new NodeSDK({
+  traceExporter: new OTLPTraceExporter({
+    url: 'http://collector:4318/v1/traces',
+  }),
+  instrumentations: [getNodeAutoInstrumentations()],
+});
+
+sdk.start();
+```
+
+## Configure the OpenTelemetry Collector
+
+Create a collector-config.yaml file at the root:
+
+```yaml
+# collector-config.yaml
+receivers:
+  otlp:
+    protocols:
+      http:
+
+exporters:
+  logging:
+    loglevel: debug
+  jaeger:
+    endpoint: jaeger:14250
+    tls:
+      insecure: true
+
+service:
+  pipelines:
+    traces:
+      receivers: [otlp]
+      exporters: [logging, jaeger]
+```
+
+## Add Docker Compose Configuration
+
+Create the `docker-compose.yaml` file:
+
+```yaml
+version: '3.9'
+
+services:
+  app:
+    build: ./app
+    ports:
+      - "3000:3000"
+    environment:
+      - NODE_ENV=development
+    depends_on:
+      - collector
+
+  collector:
+    image: otel/opentelemetry-collector:latest
+    volumes:
+      - ./collector-config.yaml:/etc/otelcol/config.yaml
+    command: ["--config=/etc/otelcol/config.yaml"]
+    ports:
+      - "4318:4318" # OTLP
+
+  jaeger:
+    image: jaegertracing/all-in-one:latest
+    ports:
+      - "16686:16686" # UI
+      - "14250:14250" # Collector gRPC
+```
+
+Now, add the `Dockerfile` inside the `app/` folder:
+
+```dockerfile
+# app/Dockerfile
+FROM node:18
+
+WORKDIR /usr/src/app
+COPY . .
+RUN npm install
+
+CMD ["node", "app.js"]
+```
+
+## Start the Stack
+
+Start all services with Docker Compose:
+
+```bash
+docker compose up --build
+```
+
+Once the services are running:
+
+Visit your app at [http://localhost:3000](http://localhost:3000)
+
+View traces at [http://localhost:16686](http://localhost:16686) in the Jaeger UI
+
+## Verify Traces in Jaeger
+
+After visiting your app's root endpoint, open Jaeger’s UI, search for the service (default is usually unknown_service unless explicitly named), and check the traces.
+
+You should see spans for the HTTP request, middleware, and auto-instrumented libraries.
+
+## Conclusion
+
+You now have a fully functional OpenTelemetry setup using Docker Compose. You've instrumented a basic JavaScript app to export traces and visualized them using Jaeger. This architecture is extendable for more complex applications and observability pipelines using Prometheus, Grafana, or cloud-native exporters.
+
+For advanced topics such as custom span creation, metrics, and logs, consult the OpenTelemetry JavaScript docs.