OpenTelemetry

OpenTelemetry (OTel) is a standard/toolset for observability. It helps your application collect traces, metrics, and logs and send them to monitoring systems.

It’s a collector for traces.

Think of it as the instrumentation layer between your application and observability tools.

Your application
      │
      │ OpenTelemetry
      ▼
┌─────────────────┐
│ Traces           │
│ Metrics          │
│ Logs             │
└─────────────────┘
      │
      ▼
Observability system
(OpenSearch, Jaeger, Grafana, etc.)

For your tracing example

Suppose:

POST /orders

OpenTelemetry can automatically create a trace:

Trace ID: abc123
 
POST /orders
   │
   ├── authenticate user
   │
   ├── create order
   │     └── PostgreSQL query
   │
   ├── call payment API
   │
   └── publish notification

Each operation can become a span:

Trace abc123
│
├── HTTP POST /orders       ← span
├── PostgreSQL INSERT       ← span
├── Payment API request     ← span
└── RabbitMQ publish        ← span

The important part is that OpenTelemetry can propagate the trace context between these operations/services, so you can connect them back to the original request.

Why use it?

Without tracing, you might have:

ERROR payment failed
ERROR database timeout
INFO order created

and wonder:

“Are these related?”

With OpenTelemetry:

trace_id = abc123

you can see that all those operations belong to the same request.

OpenTelemetry vs OpenSearch

They are not the same thing:

OpenTelemetry	OpenSearch
Collects/instruments telemetry	Stores and searches data
Creates traces/spans	Indexes data
Collects metrics	Lets you query/analyze it
Can collect logs	Provides dashboards
Sends data elsewhere	Receives/stores data

So a typical setup could be:

Express application
       │
       ▼
 OpenTelemetry
       │
       ▼
Telemetry Collector
       │
       ├──► OpenSearch
       ├──► Prometheus
       └──► Jaeger

Mental model:

OpenTelemetry = “How do I observe what my application is doing?”
OpenSearch = “Where do I store/search/analyze that information?”

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Back-End