Monitoring Legacy PHP Applications

Minimum monitoring for any production PHP app: an uptime/synthetic check on key pages, PHP-FPM status metrics (active processes, listen queue, max children reached), error-rate alerts from logs or an error tracker, database slow query monitoring, and server resources. APM tools (New Relic, Datadog, Elastic APM, OpenTelemetry PHP) add traces with little code change.

# Nginx: expose FPM status internally for the metrics exporter
location ~ ^/(fpm-status|fpm-ping)$ {
    allow 127.0.0.1;
    deny all;
    fastcgi_pass unix:/run/php/php7.4-fpm.sock;
    include fastcgi_params;
    fastcgi_param SCRIPT_FILENAME $fastcgi_script_name;
}

Common pitfalls

• Alerting on every error log line (alert fatigue).
• Public FPM status endpoints.
• No alert when 'max children reached' indicates saturation.

Key points

• Uptime checks + error-rate alerts
• Watch FPM saturation
• APM for traces

Further reading: PHP manual: FPM status page