Logging

Log Locations

Service	Log Path
Nginx	/var/log/nginx/access.log, error.log
Supervisor	/var/log/supervisor/
Docker	docker logs <container>
Systemd	journalctl -u <service>
PHP-FPM	/var/log/php-fpm/

Basic Commands

# Tail logs in real-time
tail -f /var/log/nginx/access.log

# Last 100 lines
tail -n 100 /var/log/nginx/error.log

# Search logs
grep "error" /var/log/nginx/error.log
grep -i "500" /var/log/nginx/access.log

# Journalctl (systemd)
journalctl -u snapcode -f
journalctl -u snapcode --since "1 hour ago"

Log Rotation

/etc/logrotate.d/snapcode:

/var/log/snapcode/*.log {
    daily
    rotate 14
    compress
    delaycompress
    missingok
    notifempty
    create 0640 www-data www-data
    postrotate
        systemctl reload snapcode > /dev/null 2>&1 || true
    endscript
}

Docker Logging

# View logs
docker logs snapcode
docker logs -f snapcode          # Follow
docker logs --tail 100 snapcode  # Last 100

# Docker Compose
docker-compose logs -f snapcode

Structured Logging (JSON)

import json
import logging

class JSONFormatter(logging.Formatter):
    def format(self, record):
        return json.dumps({
            'timestamp': self.formatTime(record),
            'level': record.levelname,
            'message': record.getMessage(),
            'module': record.module
        })

Log Levels

Level	Use Case
DEBUG	Development details
INFO	General information
WARNING	Potential issues
ERROR	Errors that need attention
CRITICAL	System failures

Centralized Logging (ELK)

App → Filebeat → Logstash → Elasticsearch → Kibana

For small projects, start with file-based logging and tail -f.