PHP Observability

Also Known As

TL;DR

Explanation

PHP observability toolkit: Logs (Monolog with structured JSON handlers — Loki, Elasticsearch, Datadog), Metrics (prometheus/client_php — expose /metrics for Prometheus scraping; StatsD for push-based metrics), Traces (opentelemetry-php or Datadog ddtrace auto-instrumentation — distributed tracing across services). PHP-specific considerations: PHP-FPM process-per-request model means metrics must persist across requests (shared memory via APCu or push to StatsD). Correlation IDs: generate a UUID per request, pass it in all log entries and outgoing HTTP headers — enables correlating logs, metrics, and traces for a single request.

Common Misconception

Why It Matters

Common Mistakes

• No correlation IDs — cannot connect related events across log lines and services.
• Logging without structure — plain text logs cannot be queried for specific fields.
• Metrics without labels — unlabelled counters cannot distinguish between endpoints.
• No request duration histogram — cannot calculate p95/p99 latency without it.

Code Examples

// Plain text logs — unsearchable:
error_log('Error processing order ' . $id . ' for user ' . $userId);
// Cannot query: all errors for user 42
// Cannot correlate with database traces
// Cannot alert when error rate exceeds threshold

// Structured observability:
// 1. Structured logging:
$logger->error('order.processing.failed', [
    'order_id'    => $id,
    'user_id'     => $userId,
    'trace_id'    => $this->traceId,
    'duration_ms' => $elapsed,
]);

// 2. Metrics:
$counter->labels(['endpoint' => 'checkout', 'status' => '500'])->inc();
$histogram->labels(['endpoint' => 'checkout'])->observe($duration);

// 3. Trace propagation:
$span = $tracer->spanBuilder('order.process')->startSpan();
$span->setAttribute('order.id', $id);
finally { $span->end(); }

References

• ↗ https://opentelemetry.io/docs/languages/php/

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