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Effective monitoring and troubleshooting of your Nginx server ensures high availability, performance, and quick resolution of issues. In this guide, we’ll cover:
  • Collecting and interpreting access and error logs
  • Exposing and querying basic metrics with the stub_status module
  • Integrating with external monitoring platforms
  • Safely testing and reloading configurations
  • Checking service health and firewall settings

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HTTP Access Logs

Nginx’s HTTP access logs record every client request. By default, logs are written in the combined format, but you can define a custom pattern in the http block. 
http {
    log_format custom '$remote_addr - $remote_user [$time_local] "$request" '
                      '$status $body_bytes_sent "$http_referer" '
                      '"$http_user_agent" "$http_x_forwarded_for"';
}
The image lists log format options with descriptions for each, such as client IP address, authenticated user, request details, status code, and more.
Defining a custom log format lets you include only the fields you need, simplifying downstream parsing and analytics.

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Common Log Variables

VariableDescription
$remote_addrClient IP address
$remote_userAuthenticated username (or - if none)
$time_localLocal timestamp
$requestRequest line (METHOD URI HTTP/VERSION)
$statusResponse status code (e.g., 200, 404)
$body_bytes_sentBytes sent to the client
$http_refererReferring URL
$http_user_agentClient browser user agent
$http_x_forwarded_forOriginal client IP when behind proxies

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Enabling and Viewing Access Logs

  1. Enable in your server block: 
    server {
    listen 80;
    server_name example.com www.example.com;

    root /var/www/example.com/html;
    index index.html;

    access_log /var/log/nginx/access.log custom;
    error_log  /var/log/nginx/error.log;

    location / {
        try_files $uri $uri/ =404;
    }
}
  2. Tail the log to observe incoming requests: 
    cd /var/log/nginx/
tail -F access.log
Example entry (using the custom format): 
192.168.1.1 - - [26/Jan/2025:14:23:35 +0000] "GET /images/logo.png HTTP/1.1" 200 512 "-" "Mozilla/5.0…Chrome/91.0…Safari/537.36"
Mapping fields:
  • 192.168.1.1 → $remote_addr
  • - → $remote_user
  • [26/Jan/2025:14:23:35 +0000] → $time_local
  • “GET /images/logo.png HTTP/1.1” → $request
  • 200 → $status
  • 512 → $body_bytes_sent
  • ”-” → $http_referer
  • “Mozilla/5.0…Safari/537.36” → $http_user_agent

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Error Logs

Error logs capture configuration syntax errors, runtime exceptions, and worker process messages. Enable them alongside access logs: 
server {
    listen 80;
    server_name example.com www.example.com;

    root /var/www/example.com/html;
    index index.html;

    access_log /var/log/nginx/access.log custom;
    error_log  /var/log/nginx/error.log warn;

    location / {
        try_files $uri $uri/ =404;
    }
}
Monitor errors in real time: 
cd /var/log/nginx/
tail -F error.log
Example log entries: 
2025/01/29 23:44:57 [emerg] 71265#71265: invalid number of arguments in "root" directive in /etc/nginx/sites-enabled/default:24
2025/01/29 23:46:03 [emerg] 71439#71439: "server" directive is not allowed here in /etc/nginx/sites-enabled/default:39
Frequent [emerg] or [crit] entries usually point to misconfigurations that need immediate attention.

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HTTP Stub Status Metrics

The stub_status module provides a lightweight metrics endpoint for basic Nginx statistics. 
server {
    listen       81;
    server_name  localhost;

    location /nginx_status {
        stub_status;
        access_log off;
        allow 127.0.0.1;
        deny all;
    }
}
  • Port 81 isolates the status endpoint
  • access_log off reduces noise
  • allow/deny restricts access to localhost
Fetch metrics: 
curl http://127.0.0.1:81/nginx_status
Sample output: 
Active connections: 309
server accepts handled requests
16630948 16630948 31070465
Reading: 11 Writing: 218 Waiting: 38
MetricMeaning
Active connectionsCurrently open client connections
acceptsTotal accepted connections
handledConnections handled (usually = accepts)
requestsTotal processed requests
ReadingConnections reading client requests
WritingConnections writing responses
WaitingIdle keep-alive connections

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External Monitoring Agents

For advanced dashboards, alerts, and long-term retention, integrate Nginx with external platforms.
ToolUse CaseLink
Prometheus & GrafanaPulls stub_status metrics, rich graphsPrometheus / Grafana
DatadogSaaS monitoring with Nginx integrationDatadog
DynatraceFull-stack application monitoringDynatrace
New RelicAPM with Nginx pluginNew Relic
After installing the Datadog agent, you’ll receive out-of-the-box metrics for CPU, memory, disk I/O, network, requests, connections, and status codes.
The image shows a dashboard of Data Dog System Metrics, displaying various system performance graphs such as CPU usage, memory usage, disk latency, network traffic, and connection rates.
The image shows an Nginx dashboard displaying various metrics such as requests per second, active connections, and logs. It includes graphs, a map of requests by host, and a log list.

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Configuration Testing and Reloading

Validate every change before reloading Nginx: 
nginx -t
Success: 
nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
nginx: configuration file /etc/nginx/nginx.conf test is successful
Failure: 
nginx: [emerg] unknown directive "worker_connection" in /etc/nginx/nginx.conf:7
nginx: configuration file /etc/nginx/nginx.conf test failed
Always run nginx -t prior to nginx -s reload to prevent downtime due to syntax errors.
Reload without dropping connections: 
nginx -s reload

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Service Status and Basic Connectivity

Check Nginx’s systemd status: 
systemctl status nginx
If it’s inactive: 
systemctl start nginx
Ensure no port conflicts on 80 or 443: 
ss -tulpn | grep nginx
Test HTTP locally: 
curl -I http://localhost
A 200 OK confirms that Nginx is serving content correctly.

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Firewall Configuration

Open ports 80 and 443 on both OS and cloud firewalls. Ubuntu (ufw): 
sudo ufw allow 80/tcp
sudo ufw allow 443/tcp
sudo ufw reload
RHEL/CentOS (firewalld): 
sudo firewall-cmd --permanent --add-port=80/tcp
sudo firewall-cmd --permanent --add-port=443/tcp
sudo firewall-cmd --reload
Blocked ports will prevent any external traffic from reaching your server.

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Conclusion

You’ve learned how to:
  • Define and interpret access and error logs
  • Expose basic metrics with stub_status
  • Integrate with external monitoring tools (e.g., Datadog, Prometheus)
  • Validate and reload configurations safely
  • Verify service status, connectivity, and firewall settings
With these practices in place, your Nginx server will be easier to monitor, troubleshoot, and maintain.

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