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Initial setup, cleanup, VPS setup

2026-03-07 23:11:31 +02:00

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Logging Configuration Guide

Overview

The application uses Logback for logging with the following features:

Runtime log level changes (scan every 30 seconds)
Asynchronous file logging (non-blocking I/O for high concurrency)
Automatic log rotation (50MB per file, 14 days retention, 10GB total cap)
External configuration file (editable on VPS without rebuilding)

Log File Location

Default Location

Logs are stored in: ./logs/ directory (relative to where the JAR is executed)

Custom Location

Set the LOG_DIR environment variable or system property:

export LOG_DIR=/var/log/lottery-be
java -jar lottery-be.jar

Or:

java -DLOG_DIR=/var/log/lottery-be -jar lottery-be.jar

Log File Naming

Current log: logs/lottery-be.log
Rolled logs: logs/lottery-be-2024-01-15.0.log, logs/lottery-be-2024-01-15.1.log, etc.
Max file size: 50MB per file
Retention: 14 days
Total size cap: 10GB

Using External logback-spring.xml on VPS

By default, logback-spring.xml is packaged inside the JAR. To use an external file on your VPS:

Step 1: Copy logback-spring.xml to VPS

# Copy from JAR (if needed) or from your source code
# Place it in a location like: /opt/lottery-be/config/logback-spring.xml
# Or next to your JAR: /opt/lottery-be/logback-spring.xml

Step 2: Start application with external config

# Option 1: System property
java -Dlogging.config=/opt/lottery-be/logback-spring.xml -jar lottery-be.jar

# Option 2: Environment variable
export LOGGING_CONFIG=/opt/lottery-be/logback-spring.xml
java -jar lottery-be.jar

# Option 3: In systemd service file
[Service]
Environment="LOGGING_CONFIG=/opt/lottery-be/logback-spring.xml"
ExecStart=/usr/bin/java -jar /opt/lottery-be/lottery-be.jar

Step 3: Edit logback-spring.xml on VPS

# Edit the file
nano /opt/lottery-be/logback-spring.xml

# Change log level (example: change com.lottery from INFO to DEBUG)
# Find: <logger name="com.lottery" level="INFO"/>
# Change to: <logger name="com.lottery" level="DEBUG"/>

# Save and exit
# Logback will automatically reload within 30 seconds (scanPeriod="30 seconds")

Linux Commands for Log Management

Find Log Files

# Find all log files
find /opt/lottery-be -name "*.log" -type f

# Find logs in default location
ls -lh ./logs/

# Find logs with custom LOG_DIR
ls -lh /var/log/lottery-be/

View Log Files

# View current log file (real-time)
tail -f logs/lottery-be.log

# View last 100 lines
tail -n 100 logs/lottery-be.log

# View with line numbers
cat -n logs/lottery-be.log | less

# View specific date's log
cat logs/lottery-be-2024-01-15.0.log

Search Logs

# Search for errors
grep -i "error" logs/lottery-be.log

# Search for specific user ID
grep "userId=123" logs/lottery-be.log

# Search across all log files
grep -r "ERROR" logs/

# Search with context (5 lines before/after)
grep -C 5 "ERROR" logs/lottery-be.log

# Search and highlight
grep --color=always "ERROR\|WARN" logs/lottery-be.log | less -R

Monitor Logs in Real-Time

# Follow current log
tail -f logs/lottery-be.log

# Follow and filter for errors only
tail -f logs/lottery-be.log | grep -i error

# Follow multiple log files
tail -f logs/lottery-be*.log

# Follow with timestamps
tail -f logs/lottery-be.log | while read line; do echo "[$(date '+%Y-%m-%d %H:%M:%S')] $line"; done

Check Log File Sizes

# Check size of all log files
du -sh logs/*

# Check total size of logs directory
du -sh logs/

# List files sorted by size
ls -lhS logs/

# Check disk space
df -h

Clean Old Logs

# Logback automatically deletes logs older than 14 days
# But you can manually clean if needed:

# Remove logs older than 7 days
find logs/ -name "*.log" -mtime +7 -delete

# Remove logs older than 14 days (matching logback retention)
find logs/ -name "*.log" -mtime +14 -delete

Changing Log Level at Runtime

Method 1: Edit logback-spring.xml (Recommended)

Edit the external logback-spring.xml file:
```
nano /opt/lottery-be/logback-spring.xml
```

Change the logger level (example: enable DEBUG for entire app):

<!-- Change from: -->
<logger name="com.lottery" level="INFO"/>

<!-- To: -->
<logger name="com.lottery" level="DEBUG"/>

Save the file. Logback will automatically reload within 30 seconds.

Verify the change:

tail -f logs/lottery-be.log
# You should see DEBUG logs appearing after ~30 seconds

Method 2: Change Specific Logger

To change only a specific service (e.g., GameRoomService):

<!-- In logback-spring.xml, change: -->
<logger name="com.lottery.lottery.service.GameRoomService" level="WARN"/>

<!-- To: -->
<logger name="com.lottery.lottery.service.GameRoomService" level="DEBUG"/>

Method 3: Change Root Level

To change the root level for all loggers:

<!-- In logback-spring.xml, change: -->
<root level="INFO">

<!-- To: -->
<root level="DEBUG">

Note: This will generate A LOT of logs. Use with caution in production.

Log Levels Explained

ERROR: Critical errors that need immediate attention
WARN: Warnings that might indicate problems
INFO: Important application events (round completion, payments, etc.)
DEBUG: Detailed debugging information (very verbose, use only for troubleshooting)

Default Configuration

Root level: INFO
Application (com.lottery): INFO
High-traffic services: WARN (GameRoomService, GameWebSocketController)
Infrastructure packages: WARN (Spring, Hibernate, WebSocket, etc.)

Performance Considerations

Asynchronous logging: Logs are written asynchronously to prevent blocking main threads
Queue size: 256 log entries (good for 1000+ concurrent users)
Never block: If queue is full, lower-level logs (DEBUG/INFO) may be dropped, but WARN/ERROR are always kept
File I/O: All file writes are non-blocking

Troubleshooting

Logs not appearing

Check log file location:
```
ls -la logs/
```

Check file permissions:

ls -l logs/lottery-be.log
# Ensure the application user has write permissions

Check disk space:
```
df -h
```

Log level changes not taking effect

Verify scan is enabled in logback-spring.xml:

<configuration scan="true" scanPeriod="30 seconds">

Check for syntax errors in logback-spring.xml:

# Logback will log errors to console if config is invalid

Restart application if needed (shouldn't be necessary with scan enabled)

Too many logs / Out of memory

Increase log level to WARN:
```
<root level="WARN">
```
Check log file sizes:
```
du -sh logs/*
```
Clean old logs manually if needed

Example: Enabling DEBUG for Troubleshooting

Edit logback-spring.xml:

nano /opt/lottery-be/logback-spring.xml

Change specific logger to DEBUG:

<logger name="com.lottery.lottery.service.GameRoomService" level="DEBUG"/>

Save and wait 30 seconds

Monitor logs:

tail -f logs/lottery-be.log | grep "GameRoomService"

After troubleshooting, change back to WARN:

<logger name="com.lottery.lottery.service.GameRoomService" level="WARN"/>

Systemd Service Example

If using systemd, here's an example service file:

[Unit]
Description=Lottery Backend Application
After=network.target

[Service]
Type=simple
User=lottery
WorkingDirectory=/opt/lottery-be
Environment="LOGGING_CONFIG=/opt/lottery-be/logback-spring.xml"
Environment="LOG_DIR=/var/log/lottery-be"
ExecStart=/usr/bin/java -jar /opt/lottery-be/lottery-be.jar
Restart=always
RestartSec=10

[Install]
WantedBy=multi-user.target

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