Checkout Failure Incident

Common Checkout Failures

Failure Types:
├── Payment gateway timeout
├── Payment declined
├── Inventory reservation failure
├── Address validation error
├── Tax calculation error
├── Shipping method unavailable
├── Cart session expired
└── Server error (500)

Impact:
├── Lost sales
├── Customer frustration
├── Cart abandonment
└── Revenue loss

Detection Signals

// Monitor these metrics
$metrics = [
    'checkout_error_rate' => '> 1%',
    'payment_failure_rate' => '> 5%',
    'checkout_latency_p99' => '> 5000ms',
    'cart_abandonment_rate' => '> 70%',
    'order_completion_rate' => '< 30%'
];

// Alert configuration
$alerts = [
    'checkout_errors' => [
        'metric' => 'checkout_error_count',
        'threshold' => 10,
        'period' => '5m',
        'severity' => 'critical'
    ],
    'payment_failures' => [
        'metric' => 'payment_failure_count',
        'threshold' => 20,
        'period' => '5m',
        'severity' => 'critical'
    ]
];

Step 1: Gather Information

# Check error logs
tail -f /var/log/magento/exception.log
tail -f /var/log/magento/payment.log

# Check application logs
grep -i 'checkout' /var/log/magento/system.log
grep -i 'payment' /var/log/magento/system.log

# Check web server logs
tail -f /var/log/nginx/access.log | grep checkout
tail -f /var/log/nginx/error.log

# Check database
SHOW PROCESSLIST;
SHOW ENGINE INNODB STATUS;

Step 2: Identify Symptoms

$errorPatterns = [
    'Payment timeout' => 'payment_gateway_timeout',
    'Card declined' => 'card_declined',
    'Inventory unavailable' => 'insufficient_stock',
    'Address invalid' => 'address_validation_failed',
    'Session expired' => 'cart_session_expired'
];

// Query recent checkout errors
$errors = $this->db->fetchAll(
    "SELECT error_type, COUNT(*) as count 
     FROM checkout_errors 
     WHERE created_at > DATE_SUB(NOW(), INTERVAL 1 HOUR) 
     GROUP BY error_type 
     ORDER BY count DESC"
);

Step 3: Analyze Root Cause

// Common root causes
$rootCauses = [
    'Payment gateway' => [
        'API timeout',
        'Invalid credentials',
        'Rate limiting',
        'Network issue'
    ],
    'Inventory' => [
        'Stock not reserved',
        'Race condition',
        'Reservation expired',
        'Stock sync delay'
    ],
    'Session' => [
        'Redis failure',
        'Session timeout',
        'Cookie issue',
        'Load balancer issue'
    ],
    'Server' => [
        'PHP memory limit',
        'MySQL timeout',
        'Redis timeout',
        'Disk full'
    ]
];

Immediate Actions

// 1. Enable maintenance mode (if needed)
public function enableMaintenanceMode()
{
    $this->config->save('maintenance_mode', 1);
    // Show maintenance page
}

// 2. Scale up servers
public function scaleUpServers()
{
    // Add more PHP-FPM workers
    $this->deployment->scale('php-fpm', 5);
    
    // Add more MySQL read replicas
    $this->database->addReadReplica();
}

// 3. Switch to fallback payment
public function enableFallbackPayment()
{
    $this->config->save('payment/stripe/active', 0);
    $this->config->save('payment/paypal/active', 1);
}

// 4. Flush caches
public function flushCaches()
{
    $this->cache->flush();
    $this->cache->clean();
    $this->varnish->purge();
}

Fix Implementation

// Example: Fix payment gateway timeout
public function fixPaymentGatewayTimeout()
{
    // 1. Increase timeout
    $this->config->save('payment/stripe/timeout', 30);
    
    // 2. Add retry logic
    $this->paymentService->setRetryAttempts(3);
    $this->paymentService->setRetryDelay(1000);
    
    // 3. Add circuit breaker
    $this->circuitBreaker->configure([
        'failure_threshold' => 5,
        'recovery_timeout' => 60,
        'half_open_max' => 3
    ]);
    
    // 4. Monitor and alert
    $this->monitoring->addMetric('payment_gateway_latency');
    $this->monitoring->addAlert([
        'metric' => 'payment_gateway_latency',
        'threshold' => 5000,
        'action' => 'notify'
    ]);
}

Verification

// Test checkout flow
public function testCheckoutFlow()
{
    // Create test order
    $order = $this->createTestOrder();
    
    // Process payment
    $result = $this->paymentService->process($order);
    
    // Verify success
    if ($result->isSuccess()) {
        $this->logger->info('Checkout test passed');
    } else {
        $this->logger->error('Checkout test failed: ' . $result->getMessage());
    }
    
    // Check metrics
    $metrics = $this->monitoring->getMetrics();
    if ($metrics['checkout_error_rate'] < 1) {
        $this->logger->info('Error rate normalized');
    }
}

Communication

// Status page update
public function updateStatusPage($status, $message)
{
    $this->statusPage->update([
        'status' => $status,
        'message' => $message,
        'timestamp' => time()
    ]);
}

// Customer notification
public function notifyCustomers($affectedOrders)
{
    foreach ($affectedOrders as $order) {
        $this->emailService->send(
            $order->getCustomerEmail(),
            'checkout_issue',
            ['order' => $order]
        );
    }
}

Monitoring Setup

// Comprehensive monitoring
$monitoring = [
    'checkout_flow' => [
        'metrics' => ['success_rate', 'error_rate', 'latency'],
        'alerts' => [
            'error_rate > 1%' => 'critical',
            'latency_p99 > 5000ms' => 'warning'
        ]
    ],
    'payment_gateway' => [
        'metrics' => ['success_rate', 'failure_rate', 'response_time'],
        'alerts' => [
            'failure_rate > 5%' => 'critical',
            'response_time > 3000ms' => 'warning'
        ]
    ],
    'inventory' => [
        'metrics' => ['reservation_success', 'stock_available'],
        'alerts' => [
            'reservation_failures > 10/hour' => 'critical'
        ]
    ]
];

Testing Strategy

// Automated checkout tests
public function testCheckoutScenarios()
{
    $scenarios = [
        'guest_checkout',
        'customer_checkout',
        'multiple_payment_methods',
        'coupon_code',
        'gift_card',
        'virtual_product',
        'downloadable_product',
        'bundle_product'
    ];
    
    foreach ($scenarios as $scenario) {
        $this->runCheckoutTest($scenario);
    }
}

// Load testing
public function testCheckoutUnderLoad()
{
    $this->loadTester->run([
        'concurrent_users' => 1000,
        'duration' => '10m',
        'target' => '/checkout'
    ]);
}

Runbook

# Checkout Failure Runbook

## Detection
- Monitor checkout error rate
- Monitor payment failure rate
- Monitor cart abandonment rate

## Investigation
1. Check error logs
2. Check payment gateway status
3. Check inventory levels
4. Check server resources

## Mitigation
1. Scale servers if load issue
2. Switch payment gateway if timeout
3. Flush caches if stale data

## Resolution
1. Fix root cause
2. Verify with tests
3. Monitor metrics

## Prevention
1. Add monitoring
2. Write runbook
3. Conduct postmortem