Practical guides to quickly identify and resolve common problems.
When an alert arrives, every minute counts. The time between detecting an incident and resolving it determines the impact on your users and business. Quick, methodical diagnosis can make the difference between a micro-interruption and a catastrophic outage.
Server errors are often intimidating: cryptic messages, incomprehensible stack traces, logs scattered across multiple machines. Yet, with the right methodology, most problems can be identified and resolved in minutes.
These diagnostic guides were created by production engineers who have managed thousands of incidents. They follow a systematic approach: identify symptoms, isolate the cause, apply the solution, and prevent recurrence. Combine proactive monitoring with MoniTao and structured diagnosis to minimize the impact of every incident.
Effectively diagnosing a web incident presents several challenges:
Here are the most frequent server errors and their typical causes:
Check our specific guides for each error type:
Follow this systematic approach for any incident:
Here are the most useful commands for diagnosing an incident:
# Check recent web server errors
tail -100 /var/log/nginx/error.log
# Search for 5xx errors in access logs
grep " 5[0-9][0-9] " /var/log/nginx/access.log | tail -50
# Check PHP-FPM worker status
systemctl status php-fpm
cat /var/log/php-fpm/error.log | tail -50
# Check system resources
top -bn1 | head -20
free -h
df -h
# Check network connections
ss -tuln | grep LISTEN
netstat -an | grep ESTABLISHED | wc -l
# Database logs (MySQL)
tail -50 /var/log/mysql/error.logThese commands quickly assess the state of the web server, application, and system resources. Start with error logs, then expand your investigation based on clues found.
Start by qualifying the incident (scope, impact), then check the web server error logs. They usually contain the first clues: error code, timestamp, and often a descriptive message.
Server logs (access.log, error.log) are your first source. Then: top/htop for resources, ss/netstat for network, and specific logs for each service (PHP-FPM, MySQL, etc.).
Prepare runbooks documenting diagnosis and resolution for common errors. Train the team to use them. Automate what can be automated (diagnostic scripts, enriched alerts).
MoniTao detects the problem and provides initial context: error code, response time, exact timestamp. Deep diagnosis requires access to server logs, which MoniTao cannot view.
First check system metrics (CPU, memory). If they're normal, the problem is probably application-level. If they're saturated, it's infrastructure. Application logs then give more details.
No, restarting can erase valuable information for diagnosis. First capture logs, metrics and system state. Only restart after collecting data or if urgency requires it.
Effective diagnosis relies on structured methodology and good knowledge of your tech stack. Minutes invested in understanding a problem are always worthwhile: they prevent recurrence and enrich team documentation.
MoniTao helps you detect incidents quickly and provides initial context. Combined with these diagnostic guides, you have all the tools to minimize the impact of every incident on your users.
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