Nginx Monitoring Guide: Key Metrics, Alerts & Tools (2026)

# /etc/nginx/conf.d/status.conf
server {
    listen 127.0.0.1:8080;
    server_name _;

    location /nginx_status {
        stub_status on;
        access_log off;
        allow 127.0.0.1;
        deny all;
    }
}

# Test and reload
nginx -t && nginx -s reload

# Output at http://localhost:8080/nginx_status:
# Active connections: 42
# server accepts handled requests
#  15234 15234 78901
# Reading: 1 Writing: 8 Waiting: 33

# Docker Compose example
version: '3'
services:
  nginx-exporter:
    image: nginx/nginx-prometheus-exporter:1.1
    command:
      - --nginx.scrape-uri=http://nginx:8080/nginx_status
    ports:
      - "9113:9113"
    depends_on:
      - nginx

# Prometheus scrape config
scrape_configs:
  - job_name: 'nginx'
    static_configs:
      - targets: ['localhost:9113']
    scrape_interval: 15s

# Key metrics exposed:
# nginx_connections_active
# nginx_connections_accepted_total
# nginx_connections_handled_total
# nginx_http_requests_total
# nginx_up (1 = healthy, 0 = can't reach nginx)

groups:
  - name: nginx
    rules:
      # Nginx is down
      - alert: NginxDown
        expr: nginx_up == 0
        for: 1m
        labels:
          severity: critical
        annotations:
          summary: "Nginx is not responding"

      # Connection capacity warning (>80% of worker limit)
      - alert: NginxHighConnectionCount
        expr: nginx_connections_active > (worker_connections * worker_processes * 0.8)
        for: 5m
        labels:
          severity: warning
        annotations:
          summary: "Nginx connections approaching limit"

      # 5xx spike (requires log-based metric or Nginx Plus)
      - alert: NginxHigh5xxRate
        expr: |
          rate(nginx_http_requests_total{status=~"5.."}[5m]) /
          rate(nginx_http_requests_total[5m]) > 0.01
        for: 5m
        labels:
          severity: critical
        annotations:
          summary: "Nginx 5xx error rate > 1%"

# nginx.conf — add request_time to log format
log_format monitoring '$remote_addr - $remote_user [$time_local] '
    '"$request" $status $body_bytes_sent '
    '"$http_referer" "$http_user_agent" '
    'rt=$request_time uct=$upstream_connect_time '
    'uht=$upstream_header_time urt=$upstream_response_time';

access_log /var/log/nginx/access.log monitoring;

# Key variables:
# $request_time       — total time from first byte to last byte sent to client
# $upstream_response_time — time your backend took (excludes Nginx overhead)
# $upstream_connect_time  — TCP connect time to upstream

# Passive health check (open source)
# Marks upstream unhealthy after N consecutive failures
upstream app_servers {
    server 10.0.0.1:8000 max_fails=3 fail_timeout=30s;
    server 10.0.0.2:8000 max_fails=3 fail_timeout=30s;
    server 10.0.0.3:8000 backup;
}

# Active health check (Nginx Plus)
upstream app_servers {
    zone app_zone 64k;
    server 10.0.0.1:8000;
    server 10.0.0.2:8000;
}

server {
    location / {
        proxy_pass http://app_servers;
        health_check interval=5s fails=3 passes=2 uri=/health;
    }
}