Discord Bot Error Handling and Logging: Production Best Practices

In development, errors crash your bot and you restart it. In production serving 10,000 users, crashes mean downtime, lost data, and frustrated communities.

Crash Prevention

Global Error Handlers

// Catch unhandled promise rejections (most common crash cause)
process.on('unhandledRejection', (error) => {
    console.error('[FATAL] Unhandled rejection:', error);
    // Log to file or external service
    // Do NOT process.exit() - keep running
});

// Catch uncaught exceptions
process.on('uncaughtException', (error) => {
    console.error('[FATAL] Uncaught exception:', error);
    // This is more serious - log and consider restarting
});

// Discord.js errors
client.on('error', (error) => {
    console.error('[CLIENT] Error:', error);
});

// Shard errors
client.on('shardError', (error, shardId) => {
    console.error(`[SHARD ${shardId}] Error:`, error);
});

Command Error Handling

client.on('interactionCreate', async interaction => {
    if (!interaction.isChatInputCommand()) return;
    
    try {
        const command = commands.get(interaction.commandName);
        if (!command) return;
        
        await command.execute(interaction);
    } catch (error) {
        console.error(`Command error (${interaction.commandName}):`, error);
        
        const errorMessage = 'Something went wrong. Please try again.';
        
        if (interaction.replied || interaction.deferred) {
            await interaction.followUp({ content: errorMessage, ephemeral: true }).catch(() => {});
        } else {
            await interaction.reply({ content: errorMessage, ephemeral: true }).catch(() => {});
        }
    }
});

Structured Logging

Using Winston

const winston = require('winston');

const logger = winston.createLogger({
    level: 'info',
    format: winston.format.combine(
        winston.format.timestamp(),
        winston.format.json()
    ),
    transports: [
        new winston.transports.File({ filename: 'error.log', level: 'error' }),
        new winston.transports.File({ filename: 'combined.log' }),
        new winston.transports.Console({
            format: winston.format.simple()
        })
    ]
});

// Usage
logger.info('Bot started', { guilds: client.guilds.cache.size });
logger.warn('Rate limited', { route: '/api/channels', retryAfter: 5000 });
logger.error('Command failed', { command: 'ban', error: error.message, guild: guildId });

What to Log

Always log:

• Bot startup/shutdown
• Errors with context
• Command usage statistics
• API rate limits
• Shard connections/disconnections

Never log:

• User tokens or credentials
• Full message content (privacy)
• Personally identifiable information unnecessarily

Log Rotation

Prevent logs from filling disk:

const { createLogger, transports } = require('winston');
require('winston-daily-rotate-file');

const transport = new transports.DailyRotateFile({
    filename: 'logs/bot-%DATE%.log',
    datePattern: 'YYYY-MM-DD',
    maxSize: '20m',
    maxFiles: '14d'  // Keep 14 days
});

Health Monitoring

Heartbeat

setInterval(() => {
    const health = {
        uptime: process.uptime(),
        memory: process.memoryUsage().heapUsed / 1024 / 1024,
        guilds: client.guilds.cache.size,
        ping: client.ws.ping,
        timestamp: new Date().toISOString()
    };
    
    logger.info('Health check', health);
    
    // Alert if memory exceeds threshold
    if (health.memory > 500) {
        logger.warn('High memory usage', health);
    }
    
    // Alert if ping is high
    if (health.ping > 500) {
        logger.warn('High latency', health);
    }
}, 60000);

Restart Recovery

After a crash and restart, detect it:

client.on('ready', () => {
    const lastShutdown = db.prepare('SELECT timestamp FROM bot_status ORDER BY id DESC LIMIT 1').get();
    if (lastShutdown) {
        const downtime = Date.now() - new Date(lastShutdown.timestamp).getTime();
        logger.info('Bot recovered', { downtimeMs: downtime });
    }
    
    db.prepare('INSERT INTO bot_status (status, timestamp) VALUES (?, ?)').run('online', new Date().toISOString());
});

Production Deployment

Deploy with PM2 for automatic restarts:

pm2 start bot.js --name "discord-bot" --max-memory-restart 500M
pm2 logs discord-bot  # View logs
pm2 monit             # Real-time monitoring

On Space-Node's Discord Bot hosting, PM2 or systemd keeps your bot running through crashes. Combined with proper error handling, your bot maintains near-perfect uptime.