Master Nginx Access and Error Log Configuration for Faster Debugging

Nginx logs are essential for statistics and troubleshooting; they consist of access_log (request logs) and error_log (error logs). Access logs capture client IP, browser, request time, etc., while error logs record failure details to help locate problems.

1. Access Log Configuration

The log_format directive defines the layout of each log entry. Example:

log_format main '$server_name $remote_addr - $remote_user [$time_local] "$request" '
                '$status $uptream_status $body_bytes_sent "$http_referer" '
                '"$http_user_agent" "$http_x_forwarded_for" '
                '$ssl_protocol $ssl_cipher $upstream_addr $request_time $upstream_response_time';

Key variables:

$server_name : virtual host name.

$remote_addr : client IP address.

$remote_user : authenticated user name (blank if none).

[$time_local] : request time with timezone.

$request : request URI and HTTP protocol.

$status : HTTP status code.

$uptream_status : upstream status code.

$body_bytes_sent : size of response body.

$http_referer : referring page.

$http_user_agent : client browser info.

$http_x_forwarded_for : original client IP when behind a reverse proxy.

$ssl_protocol and $ssl_cipher : SSL details.

$upstream_addr : upstream server address.

$request_time and $upstream_response_time : timing information.

Note: log_format must be placed inside the http block, otherwise Nginx will warn:

nginx: [warn] the "log_format" directive may be used only on "http" level in /etc/nginx/nginx.conf:9

The access_log directive specifies the log file path, format, buffer size, gzip compression, flush interval, and conditional logging:

# Default combined format
access_log /var/logs/nginx-access.log;
# Custom format with buffer and gzip
access_log /var/logs/nginx-access.log buffer=32k gzip flush=1m;
# Disable logging
access_log off;

Parameters:

path : log file location.

format : log format name (default is combined).

buffer : write buffer size (default 64k).

gzip : compress log before writing (level 1‑9, default 1).

flush : time after which buffer is flushed.

if : condition to skip logging.

2. Error Log Configuration

Error logs record failures and cannot be customized in format. The syntax is: error_log path level; path is the file location, and level can be debug, info, notice, warn, error, or crit (default error). error_log logs/error.log info; To effectively disable error logging, redirect it to /dev/null instead of using off: error_log /dev/null; The error_log directive can be placed in main, http, mail, stream, server, or location contexts.

3. Log Rotation

A Bash script can copy current logs with a date suffix and truncate the original files:

#!/bin/bash
LOGS_PATH=/usr/local/nginx/logs
YESTERDAY=$(date -d "yesterday" +%Y-%m-%d)
cp ${LOGS_PATH}/access.log ${LOGS_PATH}/access_${YESTERDAY}.log && >${LOGS_PATH}/access.log
cp ${LOGS_PATH}/error.log ${LOGS_PATH}/error_${YESTERDAY}.log && >${LOGS_PATH}/error.log

Schedule the script with cron to run daily at midnight:

0 0 * * * /usr/local/nginx/logs/NginxLogRotate.sh

This setup ensures Nginx creates a new log file each day while preserving previous logs for analysis.