# HA Database Sync Strategy

## Overview

This document explains the database synchronization strategy for the High Availability (HA) setup between Primary (Hetzner) and Secondary (Hostinger) servers.

## Current Setup (Nov 25, 2025)

- **Primary:** Hetzner Proxmox LXC - `/home/icke/traderv4`
- **Secondary:** Hostinger VPS (72.62.39.24) - `/home/icke/traderv4`
- **Database:** PostgreSQL 16-alpine
- **Database Name:** `trading_bot_v4`

## Option 1: PostgreSQL Streaming Replication (RECOMMENDED)

### What is it?
PostgreSQL's native master-slave replication using Write-Ahead Logs (WAL). Secondary automatically receives and applies all changes from primary in near real-time.

### Benefits
- **Real-time:** Changes replicate within 1-2 seconds
- **Native:** Built into PostgreSQL, no external tools
- **Automatic:** Once setup, runs continuously
- **Failover ready:** Secondary can be promoted to master instantly

### Setup Steps

#### 1. Configure Primary (Master)

```bash
# SSH to primary
ssh root@hetzner-ip

# Create replication user
docker exec trading-bot-postgres psql -U postgres -c "
CREATE USER replicator WITH REPLICATION ENCRYPTED PASSWORD 'your-strong-password-here';
SELECT * FROM pg_user WHERE usename = 'replicator';
"

# Configure postgresql.conf for replication
docker exec trading-bot-postgres bash -c "cat >> /var/lib/postgresql/data/postgresql.conf << CONF
# Replication settings
wal_level = replica
max_wal_senders = 3
wal_keep_size = 64
hot_standby = on
CONF"

# Allow replication connections from secondary
docker exec trading-bot-postgres bash -c "echo 'host replication replicator 72.62.39.24/32 md5' >> /var/lib/postgresql/data/pg_hba.conf"

# Restart PostgreSQL to apply changes
docker restart trading-bot-postgres

# Verify replication user
docker exec trading-bot-postgres psql -U postgres -c "SELECT usename, userepl FROM pg_user WHERE usename = 'replicator';"
```

#### 2. Configure Secondary (Replica)

```bash
# SSH to secondary
ssh root@72.62.39.24

cd /home/icke/traderv4

# Stop PostgreSQL if running
docker compose down postgres

# Backup existing data (if any)
sudo mv postgres-data postgres-data.backup-$(date +%Y%m%d-%H%M%S) || true

# Create base backup from primary
docker run --rm \
  -v $(pwd)/postgres-data:/var/lib/postgresql/data \
  -e PGPASSWORD='your-strong-password-here' \
  postgres:16-alpine \
  pg_basebackup -h hetzner-ip -p 5432 -U replicator -D /var/lib/postgresql/data -P -R

# Start PostgreSQL in replica mode
docker compose up -d postgres

# Wait for startup
sleep 10

# Verify replication status
docker exec trading-bot-postgres psql -U postgres -c "SELECT status, receive_start_lsn FROM pg_stat_wal_receiver;"
```

#### 3. Verify Replication

```bash
# On PRIMARY - Check replication status
docker exec trading-bot-postgres psql -U postgres -c "
SELECT 
  client_addr,
  state,
  sent_lsn,
  write_lsn,
  flush_lsn,
  replay_lsn,
  sync_state
FROM pg_stat_replication;
"

# Should show:
# - client_addr: 72.62.39.24
# - state: streaming
# - sync_state: async

# Test replication - Insert test data on PRIMARY
docker exec trading-bot-postgres psql -U postgres trading_bot_v4 -c "
CREATE TABLE IF NOT EXISTS replication_test (id SERIAL PRIMARY KEY, test_time TIMESTAMP);
INSERT INTO replication_test (test_time) VALUES (NOW());
SELECT * FROM replication_test;
"

# Check on SECONDARY (should see same data within 1-2 seconds)
ssh root@72.62.39.24 "docker exec trading-bot-postgres psql -U postgres trading_bot_v4 -c 'SELECT * FROM replication_test;'"

# Clean up test
docker exec trading-bot-postgres psql -U postgres trading_bot_v4 -c "DROP TABLE replication_test;"
```

### Monitoring Replication

```bash
# Check replication lag (run on PRIMARY)
docker exec trading-bot-postgres psql -U postgres -c "
SELECT 
  client_addr,
  state,
  pg_wal_lsn_diff(pg_current_wal_lsn(), replay_lsn) AS lag_bytes,
  EXTRACT(EPOCH FROM (NOW() - pg_last_xact_replay_timestamp())) AS lag_seconds
FROM pg_stat_replication;
"

# Healthy values:
# - lag_bytes: < 100KB
# - lag_seconds: < 5 seconds
```

## Option 2: Periodic Backup (FALLBACK)

### What is it?
Scheduled pg_dump backups copied to secondary every 6 hours via cron job.

### Benefits
- **Simple:** Easy to setup and understand
- **No config changes:** Primary runs normally
- **Cross-platform:** Works even with different PostgreSQL versions

### Drawbacks
- **Data loss window:** Up to 6 hours of trades could be lost
- **Not instant:** Secondary is always 0-6 hours behind

### Setup

```bash
# On PRIMARY - Create sync script
cat > /root/sync-database-to-secondary.sh << 'SCRIPT'
#!/bin/bash
LOG="/var/log/secondary-db-sync.log"
echo "[$(date)] Starting database sync..." >> $LOG

# Dump database
docker exec trading-bot-postgres pg_dump -U postgres trading_bot_v4 > /tmp/trading_bot_backup.sql

if [ $? -eq 0 ]; then
  echo "[$(date)] Database dump successful ($(wc -l < /tmp/trading_bot_backup.sql) lines)" >> $LOG
  
  # Copy to secondary
  scp /tmp/trading_bot_backup.sql root@72.62.39.24:/tmp/trading_bot_backup.sql
  
  if [ $? -eq 0 ]; then
    echo "[$(date)] Backup copied to secondary" >> $LOG
    
    # Restore on secondary
    ssh root@72.62.39.24 "docker exec -i trading-bot-postgres psql -U postgres -c 'DROP DATABASE IF EXISTS trading_bot_v4; CREATE DATABASE trading_bot_v4;' && docker exec -i trading-bot-postgres psql -U postgres trading_bot_v4 < /tmp/trading_bot_backup.sql"
    
    if [ $? -eq 0 ]; then
      echo "[$(date)] Database restored on secondary successfully" >> $LOG
    else
      echo "[$(date)] ERROR: Database restore failed" >> $LOG
    fi
  else
    echo "[$(date)] ERROR: Failed to copy backup to secondary" >> $LOG
  fi
else
  echo "[$(date)] ERROR: Database dump failed" >> $LOG
fi

echo "[$(date)] Sync complete" >> $LOG
SCRIPT

chmod +x /root/sync-database-to-secondary.sh

# Test it
/root/sync-database-to-secondary.sh

# Check log
tail /var/log/secondary-db-sync.log

# Setup cron (every 6 hours)
crontab -l > /tmp/crontab.backup
echo "0 */6 * * * /root/sync-database-to-secondary.sh" >> /tmp/crontab.backup
crontab /tmp/crontab.backup

# Verify cron
crontab -l | grep sync-database
```

## Code Sync (Both Options)

Code needs to be synced separately (n8n workflows, trading bot code, etc.)

```bash
# Create code sync script
cat > /root/sync-code-to-secondary.sh << 'SCRIPT'
#!/bin/bash
LOG="/var/log/secondary-code-sync.log"
echo "[$(date)] Starting code sync..." >> $LOG

rsync -avz --delete \
  --exclude 'node_modules' \
  --exclude '.next' \
  --exclude '.git' \
  --exclude 'logs/*' \
  --exclude 'postgres-data' \
  /home/icke/traderv4/ root@72.62.39.24:/home/icke/traderv4/ >> $LOG 2>&1

# Sync .env file
rsync -avz /home/icke/traderv4/.env root@72.62.39.24:/home/icke/traderv4/.env >> $LOG 2>&1

echo "[$(date)] Code sync complete" >> $LOG
SCRIPT

chmod +x /root/sync-code-to-secondary.sh

# Run daily at 3 AM
crontab -l > /tmp/crontab.backup
echo "0 3 * * * /root/sync-code-to-secondary.sh" >> /tmp/crontab.backup
crontab /tmp/crontab.backup
```

## n8n Workflow Sync

n8n workflows are stored in SQLite database or files depending on setup.

### If using SQLite (file-based)

```bash
# Find n8n database location
ssh root@72.62.39.24 "docker exec n8n ls -la /home/node/.n8n/"

# Sync n8n data directory
rsync -avz /path/to/n8n/data/ root@72.62.39.24:/path/to/n8n/data/
```

### If using PostgreSQL for n8n

n8n can use PostgreSQL - already covered by database replication above.

## Failover Procedure

### Scenario: Primary goes down, need to activate Secondary

#### 1. Promote Secondary to Master (if using streaming replication)

```bash
# SSH to secondary
ssh root@72.62.39.24

# Promote to master
docker exec trading-bot-postgres pg_ctl promote -D /var/lib/postgresql/data

# Verify it's now accepting writes
docker exec trading-bot-postgres psql -U postgres trading_bot_v4 -c "SELECT pg_is_in_recovery();"
# Should return 'f' (false = not in recovery = is master)

# Start trading bot (if not already running)
cd /home/icke/traderv4
docker compose up -d trading-bot
```

#### 2. Update Cloudflare DNS

```bash
# Via health monitor script (automatic)
# OR manually via Cloudflare API/dashboard
# Point flow.egonetix.de to 72.62.39.24
```

#### 3. When Primary recovers

```bash
# Reconfigure primary as new replica
# Then switch DNS back
# Or keep secondary as new primary (depends on data drift)
```

## Comparison

| Feature | Streaming Replication | Periodic Backup |
|---------|----------------------|-----------------|
| **Lag** | 1-2 seconds | 0-6 hours |
| **Setup Complexity** | Medium | Simple |
| **Data Loss Risk** | Minimal (seconds) | High (hours) |
| **Failover Time** | Instant | Minutes |
| **Resource Usage** | Low | Low |
| **Best For** | Production HA | Testing/Dev |

## Recommendation

**Use PostgreSQL Streaming Replication** for production HA setup:
- Real-time sync (1-2 second lag)
- Zero manual intervention needed
- Instant failover capability
- Native PostgreSQL feature (well-tested)

**Fallback to Periodic Backup** only if:
- Streaming replication setup fails
- Network between servers is unreliable
- You're just testing the HA concept

## Monitoring

Add to health monitor script:

```python
# Check replication lag
def check_replication_lag():
    result = subprocess.run([
        "docker", "exec", "trading-bot-postgres", 
        "psql", "-U", "postgres", "-t", "-c",
        "SELECT pg_wal_lsn_diff(pg_current_wal_lsn(), replay_lsn) FROM pg_stat_replication;"
    ], capture_output=True, text=True)
    
    lag_bytes = int(result.stdout.strip() or 0)
    
    if lag_bytes > 100000:  # 100KB
        send_telegram(f"⚠️ HIGH REPLICATION LAG: {lag_bytes/1024:.1f}KB")
```

## Troubleshooting

### Secondary not connecting

```bash
# Check firewall on primary
# Allow port 5432 from 72.62.39.24

# Check pg_hba.conf on primary
docker exec trading-bot-postgres cat /var/lib/postgresql/data/pg_hba.conf | grep replication

# Check logs on secondary
docker logs trading-bot-postgres
```

### Replication lag increasing

```bash
# Check network between servers
ping 72.62.39.24

# Check disk space on secondary
ssh root@72.62.39.24 "df -h"

# Check WAL sender processes
docker exec trading-bot-postgres psql -U postgres -c "SELECT * FROM pg_stat_replication;"
```

### Replication stopped

```bash
# Restart from base backup
# Follow "Configure Secondary" steps again
```