Application Metrics

Prometheus Architecture

Application ──▶ /metrics ──▶ Prometheus ──▶ Grafana
(magento)      (endpoint)    (scrape/store)  (visualize)

Magento Prometheus Setup

// composer.json
require {
    "promphp\prometheus_client_php": "^3.0"
}

// Metrics endpoint
// pub/metrics.php
use Prometheus\CollectorRegistry;
use Prometheus\RenderTextFormat;
use Prometheus\Storage\Redis;

$adapter = new Redis(['host' => 'redis']);
$registry = CollectorRegistry::getDefault($adapter);

$renderer = new RenderTextFormat();
header('Content-Type: ' . RenderTextFormat::MIME_TYPE);
echo $renderer->render($registry->getMetricFamilySamples());

Scrape Config

# prometheus.yml
scrape_configs:
  - job_name: 'magento'
    static_configs:
      - targets: ['magento:9090']
    metrics_path: '/metrics'
    scrape_interval: 15s

Prometheus Metric Types

Type       | Description              | Use Case
───────────|──────────────────────────|─────────────────────
Counter    | Monotonically increasing | Total requests, errors
Gauge      | Value that can go up/down| Active connections
Histogram  | Distribution of values   | Request duration
Summary     | Quantiles over window    | Latency percentiles

Counter Example

$counter = $registry->registerCounter(
    'magento_http_requests_total',
    'Total HTTP requests',
    ['method', 'status', 'route']
);

$counter->inc(['GET', '200', '/catalog/product/view']);

Histogram Example

$histogram = $registry->registerHistogram(
    'magento_http_request_duration_seconds',
    'HTTP request duration',
    ['method', 'route'],
    [0.01, 0.05, 0.1, 0.5, 1.0, 2.0, 5.0]
);

$histogram->observe($duration, ['GET', '/checkout']);

Gauge Example

$gauge = $registry->registerGauge(
    'magento_active_sessions',
    'Active user sessions'
);

$gauge->set($sessionCount);

Business Metrics

// Orders metrics
$ordersTotal = $registry->registerCounter(
    'magento_orders_total',
    'Total orders placed',
    ['status', 'payment_method']
);
$ordersTotal->inc(['pending', 'stripe']);

// Revenue metrics
$orderValue = $registry->registerHistogram(
    'magento_order_value_dollars',
    'Order value distribution',
    [], [10, 25, 50, 100, 250, 500, 1000]
);
$orderValue->observe($order->getTotal());

// Cart metrics
$cartCount = $registry->registerGauge(
    'magento_active_carts',
    'Active shopping carts'
);
$cartCount->set($activeCarts);

// Search metrics
$searchLatency = $registry->registerHistogram(
    'magento_search_duration_seconds',
    'Search query duration',
    ['type']
);
$searchLatency->observe($duration, ['fulltext']);

Inventory Metrics

$stockLevel = $registry->registerGauge(
    'magento_stock_level',
    'Current stock level',
    ['product_id', 'sku']
);
$stockLevel->set($qty, [$productId, $sku]);

Dashboard Panels

Panel 1: Request Rate
  - Total requests/sec
  - By status code (2xx, 4xx, 5xx)
  - By endpoint

Panel 2: Latency
  - P50, P95, P99 latency
  - Latency by endpoint

Panel 3: Errors
  - Error rate %
  - Top error endpoints
  - Error trend

Panel 4: Business
  - Orders per minute
  - Revenue per hour
  - Cart count

PromQL Queries

# Request rate
rate(magento_http_requests_total[5m])

# Error rate
rate(magento_http_requests_total{status=~"5.."}[5m])
  / rate(magento_http_requests_total[5m])

# P99 latency
histogram_quantile(0.99, 
  rate(magento_http_request_duration_seconds_bucket[5m])
)

# Orders per minute
rate(magento_orders_total[5m]) * 60

Dashboard JSON

{
  "title": "Magento Overview",
  "panels": [
    {
      "title": "Request Rate",
      "type": "graph",
      "targets": [{
        "expr": "rate(magento_http_requests_total[5m])",
        "legendFormat": "{{method}} {{status}}"
      }]
    },
    {
      "title": "Error Rate",
      "type": "singlestat",
      "targets": [{
        "expr": "rate(magento_http_requests_total{status=~'5..'}[5m]) / rate(magento_http_requests_total[5m]) * 100"
      }]
    }
  ]
}