data-backup-patterns

What this skill does

# Data Backup Patterns

Protect data with automated, tested, and recoverable backup strategies.

## Backup Strategy Framework

### The 3-2-1 Rule

- **3** copies of data (1 primary + 2 backups)
- **2** different storage media/types
- **1** offsite copy

### Backup Types

| Type | Speed | Storage | Recovery | When |
|------|-------|---------|----------|------|
| **Full** | Slow | Large | Fast | Weekly |
| **Incremental** | Fast | Small | Slow (needs chain) | Daily |
| **Differential** | Medium | Medium | Medium (needs last full) | Daily |
| **Snapshot** | Instant | Varies | Fast | Hourly |

## Database Backups

### PostgreSQL

```bash
#!/usr/bin/env bash
set -euo pipefail

DB_NAME="${DB_NAME:?}"
BACKUP_DIR="${BACKUP_DIR:-/backups}"
TIMESTAMP=$(date +%Y%m%d_%H%M%S)
BACKUP_FILE="${BACKUP_DIR}/${DB_NAME}_${TIMESTAMP}.sql.gz"

# Full backup with compression
pg_dump "$DB_NAME" \
  --format=custom \
  --compress=9 \
  --file="${BACKUP_FILE}"

# Verify backup is valid
pg_restore --list "${BACKUP_FILE}" > /dev/null

echo "Backup created: ${BACKUP_FILE} ($(du -h "${BACKUP_FILE}" | cut -f1))"
```

### Point-in-Time Recovery (WAL Archiving)

```bash
# postgresql.conf
archive_mode = on
archive_command = 'cp %p /archive/wal/%f'

# Restore to specific time
restore_command = 'cp /archive/wal/%f %p'
recovery_target_time = '2026-03-20 10:00:00'
```

### Redis

```bash
# Trigger RDB snapshot
redis-cli BGSAVE

# Or use AOF for point-in-time recovery
# redis.conf
appendonly yes
appendfsync everysec
```

## File System Backups

### Rsync-Based

```bash
#!/usr/bin/env bash
set -euo pipefail

SOURCE="/data"
DEST="/backups/daily"
LATEST="${DEST}/latest"
TIMESTAMP=$(date +%Y%m%d_%H%M%S)
TARGET="${DEST}/${TIMESTAMP}"

# Incremental backup using hard links
rsync -av --delete \
  --link-dest="${LATEST}" \
  "${SOURCE}/" "${TARGET}/"

# Update latest symlink
ln -snf "${TARGET}" "${LATEST}"

echo "Backup complete: ${TARGET}"
```

### Exclusion Patterns

```
# .backup-exclude
.git/
node_modules/
.venv/
__pycache__/
*.pyc
.env.local
*.secret
tmp/
.build/
```

## Encryption

### GPG Encryption

```bash
# Encrypt backup
gpg --symmetric --cipher-algo AES256 \
  --output "${BACKUP_FILE}.gpg" \
  "${BACKUP_FILE}"

# Decrypt for restore
gpg --decrypt "${BACKUP_FILE}.gpg" > "${BACKUP_FILE}"
```

### Age Encryption (Modern Alternative)

```bash
# Generate key pair
age-keygen -o key.txt

# Encrypt
age -r age1xxxxxx -o backup.sql.age backup.sql

# Decrypt
age -d -i key.txt backup.sql.age > backup.sql
```

## Rotation Policies

```python
from pathlib import Path
from datetime import datetime, timedelta

class BackupRotator:
    def __init__(self, backup_dir: str, keep_daily: int = 7, keep_weekly: int = 4, keep_monthly: int = 12):
        self.backup_dir = Path(backup_dir)
        self.keep_daily = keep_daily
        self.keep_weekly = keep_weekly
        self.keep_monthly = keep_monthly

    def rotate(self):
        backups = sorted(self.backup_dir.glob("*.sql.gz"), key=lambda p: p.stat().st_mtime, reverse=True)
        now = datetime.now()
        keep = set()

        # Keep recent daily
        for b in backups[:self.keep_daily]:
            keep.add(b)

        # Keep weekly (one per week)
        for week in range(self.keep_weekly):
            target = now - timedelta(weeks=week)
            closest = min(backups, key=lambda b: abs(datetime.fromtimestamp(b.stat().st_mtime) - target))
            keep.add(closest)

        # Keep monthly (one per month)
        for month in range(self.keep_monthly):
            target = now - timedelta(days=30 * month)
            closest = min(backups, key=lambda b: abs(datetime.fromtimestamp(b.stat().st_mtime) - target))
            keep.add(closest)

        # Remove the rest
        for backup in backups:
            if backup not in keep:
                backup.unlink()
```

## Cloud Storage

### S3-Compatible Upload

```bash
#!/usr/bin/env bash
set -euo pipefail

BUCKET="${BACKUP_BUCKET:?}"
PREFIX="backups/$(date +%Y/%m)"

# Upload with server-side encryption
aws s3 cp "${BACKUP_FILE}" \
  "s3://${BUCKET}/${PREFIX}/$(basename ${BACKUP_FILE})" \
  --storage-class STANDARD_IA \
  --sse AES256

# Set lifecycle policy for automatic archival
# (configure once in S3 lifecycle rules)
# 30 days → Glacier, 365 days → Deep Archive
```

## Automated Scheduling

### Cron/Launchd

```bash
# crontab
0 2 * * * /scripts/backup-daily.sh >> /var/log/backup.log 2>&1
0 3 * * 0 /scripts/backup-weekly.sh >> /var/log/backup.log 2>&1
```

```xml
<!-- ~/Library/LaunchAgents/com.backup.daily.plist -->
<plist version="1.0">
<dict>
    <key>Label</key><string>com.backup.daily</string>
    <key>ProgramArguments</key>
    <array>
        <string>/scripts/backup-daily.sh</string>
    </array>
    <key>StartCalendarInterval</key>
    <dict>
        <key>Hour</key><integer>2</integer>
        <key>Minute</key><integer>0</integer>
    </dict>
</dict>
</plist>
```

## Recovery Testing

### Automated Recovery Test

```bash
#!/usr/bin/env bash
set -euo pipefail

BACKUP_FILE="${1:?Usage: test-restore.sh <backup-file>}"
TEST_DB="restore_test_$(date +%s)"

# Restore to test database
createdb "${TEST_DB}"
pg_restore --dbname="${TEST_DB}" "${BACKUP_FILE}"

# Verify data integrity
ROW_COUNT=$(psql -t -c "SELECT count(*) FROM repos" "${TEST_DB}")
if [[ "${ROW_COUNT}" -lt 50 ]]; then
    echo "FAIL: Expected 50+ repos, got ${ROW_COUNT}"
    dropdb "${TEST_DB}"
    exit 1
fi

echo "PASS: Restored ${ROW_COUNT} repos successfully"
dropdb "${TEST_DB}"
```

## Anti-Patterns

- **Untested backups** — A backup you haven't restored is not a backup
- **No encryption for sensitive data** — Always encrypt backups at rest
- **Single location** — Follow the 3-2-1 rule
- **No rotation** — Unbounded backup growth fills storage
- **Manual-only backups** — Automate everything; manual backups get forgotten
- **No monitoring** — Alert on backup failures immediately