API Monitoring & Audit Trails 📊

Log API calls with structured logging, monitor endpoint performance, and build compliance-ready audit trails that record every user action.

What You'll Learn in This Lesson

• Build a structured API logger with severity levels
• Track request metrics: latency, error rates, throughput
• Record audit trails with before/after change snapshots
• Query audit logs by actor, action, or resource
• Design the audit_logs database schema with proper indexes

Note: PHP runs on a server. Our examples simulate PHP logic using JavaScript. To run real PHP, install PHP.

🎯 Real-World Analogy: API monitoring is like a security camera system for your application. The cameras (loggers) record everything that happens. The control room (metrics dashboard) shows live stats. The recorded footage (audit trail) provides evidence when something goes wrong — "who deleted that user account at 3 AM?"

Structured API Logging

Structured logging means each log entry is a machine-parseable object with consistent fields (timestamp, level, message, context) rather than free-text strings. This enables powerful querying: find all errors in the last hour, all requests by user X, or all slow queries over 1 second.

Try It: API Logger & Metrics

Log API requests, track performance metrics, and generate endpoint reports

Try it Yourself »

JavaScript

// API Logging & Monitoring in PHP
console.log("=== Why Monitor Your API? ===");
console.log();
console.log("  Without monitoring:");
console.log("  ❌ Don't know if endpoints are slow");
console.log("  ❌ Can't detect abuse or unusual patterns");
console.log("  ❌ No evidence for debugging production issues");
console.log("  ❌ Can't prove compliance for audits");
console.log();

// Build a structured logger
class APILogger {
  constructor() {
    this.logs = [];
    this.metrics = {};
  }

  log(l
...

Audit Trails for Compliance

An audit trail answers four questions: WHO performed WHAT action on WHICH resource and WHEN. Store before/after snapshots of changed data, the actor's IP address, and user agent. This is legally required for GDPR, SOC 2, HIPAA, and financial regulations.

Try It: Audit Trail System

Record user actions with change tracking and query by actor or resource

Try it Yourself »

JavaScript

// Audit Trail System for Compliance
console.log("=== Building an Audit Trail ===");
console.log();
console.log("  An audit trail records WHO did WHAT to WHICH resource and WHEN.");
console.log("  Required for: GDPR, SOC 2, HIPAA, PCI DSS, financial compliance.");
console.log();

class AuditTrail {
  constructor() { this.entries = []; }

  record(actor, action, resource, details) {
    let entry = {
      id: "audit_" + (this.entries.length + 1).toString().padStart(4, "0"),
      timestamp: new 
...

⚠️ Common Mistakes

⚠️

Logging sensitive data — Never log passwords, credit card numbers, or API secrets. Mask or redact sensitive fields before logging.

⚠️

Audit logs must be immutable — Never allow UPDATE or DELETE on audit_logs. Use INSERT-only with a retention policy. Admins who can modify audit logs defeat the purpose.

💡

Pro Tip: Use Monolog (PHP's standard logging library) with PSR-3 interface. It supports file, syslog, Slack, email, and external services like Datadog and Elasticsearch.

📋 Quick Reference — Monitoring

Concept	Description
PSR-3	PHP standard logging interface (Monolog)
Structured Logging	Machine-parseable log entries with context
Audit Trail	Immutable record of WHO/WHAT/WHEN/WHERE
Request ID	Unique ID to trace a request across services
Log Rotation	Archive old logs to prevent disk overflow

🎉 Lesson Complete!

You can now monitor APIs and build audit trails! Next, learn to implement role-based access control (RBAC).