debug-server

---
name: debug-server
description: "Production server debugging. TRIGGER when: не работает, not working, сервер упал, server down, ошибка на сервере, server error, PM2 error, 502, 500, бот не отвечает, bot not responding, сайт недоступен, site unreachable, логи, logs, crash, restart loop, memory leak, процесс упал, process crashed, app crashed, ECONNRESET, Cannot GET. Contains: PM2 diagnostics, Nginx debug, Node.js error patterns, server health check."
---

# Server Debug — Diagnostics

## Step 1 — Quick Diagnostics (run first)

```bash
pm2 status                    # what is running, status, restarts
pm2 logs --lines 50           # recent logs for all processes
pm2 logs name --err --lines 30 # errors only for a specific process
```

## Step 2 — By Symptoms

### 502 Bad Gateway
```bash
# Nginx cannot reach Node
pm2 status           # is the process running?
pm2 restart name     # restart
# Check if the port in nginx config matches the app port
grep -r "proxy_pass" /etc/nginx/sites-enabled/
```

### Bot Not Responding (Max/Telegram)
```bash
pm2 logs bot-name --lines 50
# Check if webhook is registered:
curl https://api.max.ru/subscriptions -H "Authorization: TOKEN"
```

### Process in Restart Loop
```bash
pm2 logs name --err   # crash reason
# Common causes:
# - syntax error in code
# - module not found (npm install not run)
# - environment variable not set
# - port occupied by another process
```

### High Memory Usage
```bash
pm2 status           # check memory column
pm2 prettylist | grep -A5 'monit' | head -30  # detailed memory/cpu
# Add limit in ecosystem.config.js:
# max_memory_restart: '200M'
```

### Port Occupied
```bash
lsof -i :3000        # who is using port 3000
kill -9 PID          # kill the process
pm2 start ecosystem.config.js
```

## Step 3 — System Logs

```bash
# Node/PM2 system logs
journalctl -u pm2-root -n 50

# Nginx access/error logs
tail -50 /var/log/nginx/error.log
tail -50 /var/log/nginx/access.log

# Disk space (often overlooked)
df -h
du -sh /var/log/pm2/*   # PM2 log sizes
```

## Step 4 — Environment Variables

```bash
# Check that .env is in place
ls -la /var/www/project/.env
cat /var/www/project/.env | grep -v "PASSWORD\|TOKEN\|SECRET"

# Is PM2 picking up env?
pm2 env 0   # env of process with id=0
```

## PM2 ecosystem.config.js — Typical Config

```js
module.exports = {
  apps: [{
    name: 'fuji-routes',
    script: 'server/index.js',
    cwd: '/var/www/fuji-routes',
    env: { NODE_ENV: 'production', PORT: 3000 },
    max_memory_restart: '200M',
    error_file: './logs/err.log',
    out_file: './logs/out.log',
    log_date_format: 'YYYY-MM-DD HH:mm:ss',
  }]
};
```

## Health Check — Quick Verification

```bash
# Check that the app responds
curl -s http://localhost:3000/api/ping
# or
curl -s https://domain.ru/api/ping

# SSL certificate
curl -vI https://domain.ru 2>&1 | grep -E "SSL|expire|subject"
```

## Recovery Checklist

- [ ] `pm2 status` — all processes online
- [ ] `pm2 logs --lines 20` — no crash errors
- [ ] Site opens in browser
- [ ] API `/ping` returns 200
- [ ] Bot responds to a test message