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# Observability

Observability in Go Micro spans logs, metrics, and traces. The goal is rapid insight into service behavior with minimal configuration.

## Core Principles

1. Structured Logs – Machine-parsable, leveled output
2. Metrics – Quantitative trends (counters, gauges, histograms)
3. Traces – Request flows across service boundaries
4. Correlation – IDs flowing through all three signals

## Logging

The default logger can be replaced. Use env vars to adjust level:

```bash
MICRO_LOG_LEVEL=debug go run main.go
```

Recommended fields:
- `service` – service name
- `version` – release identifier
- `trace_id` – propagated context id
- `span_id` – current operation id

## Metrics

Patterns:
- Emit counters for request totals
- Use histograms for latency
- Track error rates per endpoint

Example (pseudo-code):

```go
// Wrap handler to record metrics
func MetricsWrapper(fn micro.HandlerFunc) micro.HandlerFunc {
    return func(ctx context.Context, req micro.Request, rsp interface{}) error {
        start := time.Now()
        err := fn(ctx, req, rsp)
        latency := time.Since(start)
        metrics.Inc("requests_total", req.Endpoint(), errorLabel(err))
        metrics.Observe("request_latency_seconds", latency, req.Endpoint())
        return err
    }
}
```

## Tracing

Distributed tracing links calls across services.

Propagation strategy:
- Extract trace context from incoming headers
- Inject into outgoing RPC calls/broker messages
- Create spans per handler and client call

## Local Development Strategy

Start with only structured logs. Add metrics when operating multiple services. Introduce tracing once debugging multi-hop latency or failures.

## Roadmap (Planned Enhancements)

- Native OpenTelemetry exporter helpers
- Automatic handler/client wrapping for spans
- Default correlation IDs across broker messages

## Deployment Recommendations

| Scale | Suggested Stack |
|-------|-----------------|
| Dev   | Console logs only |
| Staging | Logs + basic metrics (Prometheus) |
| Prod (basic) | Logs + metrics + sampling traces |
| Prod (complex) | Full tracing + profiling + anomaly detection |

## Troubleshooting

| Symptom | Cause | Fix |
|---------|-------|-----|
| Missing trace IDs in logs | Context not propagated | Ensure wrappers add IDs |
| Metrics server empty | Endpoint not scraped | Verify Prometheus config |
| High cardinality metrics | Dynamic labels | Reduce labeled dimensions |

## Related

- [Getting Started](getting-started.md)
- [Plugins](plugins.md)
- [Architecture Decisions](architecture/index.md)