# PostgreSQL Backup (Docker)

Automated pg_dump backups for any Docker-hosted PostgreSQL instance. Retention, integrity check, and restore testing included.

---

## Inputs

```
CONTAINER_NAME=         # Docker container name (e.g., "matrix-postgres")
DB_NAME=                # Database to back up (e.g., "synapse")
DB_USER=                # Database user (e.g., "synapse")
BACKUP_DIR=             # Host directory for backups (e.g., "/opt/matrix/backups")
RETENTION_DAYS=14       # Days to keep backups
CRON_SCHEDULE="0 3 * * *"  # Daily at 3AM
```

---

## Step 1: Create Backup Directory

```bash
mkdir -p ${BACKUP_DIR}
chmod 700 ${BACKUP_DIR}
mkdir -p $(dirname ${BACKUP_DIR})/scripts
```

---

## Step 2: Create Backup Script

Create `$(dirname ${BACKUP_DIR})/scripts/pg_backup.sh`:

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

# --- Configuration (edit per service) ---
CONTAINER_NAME="${CONTAINER_NAME}"
DB_NAME="${DB_NAME}"
DB_USER="${DB_USER}"
BACKUP_DIR="${BACKUP_DIR}"
RETENTION_DAYS=${RETENTION_DAYS}

# --- Derived ---
TIMESTAMP=$(date +%Y%m%d_%H%M%S)
BACKUP_FILE="${BACKUP_DIR}/${DB_NAME}_${TIMESTAMP}.sql.gz"
LOG_FILE="${BACKUP_DIR}/backup.log"

log() {
  echo "[$(date '+%Y-%m-%d %H:%M:%S')] $1" | tee -a "${LOG_FILE}"
}

# --- Backup ---
log "Starting backup of ${DB_NAME} from ${CONTAINER_NAME}"

docker exec ${CONTAINER_NAME} pg_dump \
  -U ${DB_USER} \
  -d ${DB_NAME} \
  --format=plain \
  --no-owner \
  --no-privileges \
  | gzip > "${BACKUP_FILE}"

if [ $? -eq 0 ] && [ -s "${BACKUP_FILE}" ]; then
  SIZE=$(du -h "${BACKUP_FILE}" | cut -f1)
  log "Backup successful: ${BACKUP_FILE} (${SIZE})"
else
  log "ERROR: Backup failed or produced empty file"
  rm -f "${BACKUP_FILE}"
  exit 1
fi

# --- Retention ---
DELETED=$(find ${BACKUP_DIR} -name "${DB_NAME}_*.sql.gz" -mtime +${RETENTION_DAYS} -print -delete | wc -l)
log "Retention cleanup: removed ${DELETED} backups older than ${RETENTION_DAYS} days"

# --- Integrity ---
if gzip -t "${BACKUP_FILE}" 2>/dev/null; then
  log "Integrity check: PASS"
else
  log "ERROR: Integrity check FAILED — backup is corrupt"
  exit 1
fi

log "Backup complete."
```

Make executable:

```bash
chmod +x $(dirname ${BACKUP_DIR})/scripts/pg_backup.sh
```

---

## Step 3: Test Manually

```bash
$(dirname ${BACKUP_DIR})/scripts/pg_backup.sh
ls -lh ${BACKUP_DIR}/*.sql.gz
cat ${BACKUP_DIR}/backup.log
```

---

## Step 4: Schedule via Cron

```bash
(crontab -l 2>/dev/null; echo "${CRON_SCHEDULE} $(dirname ${BACKUP_DIR})/scripts/pg_backup.sh >> ${BACKUP_DIR}/cron.log 2>&1") | crontab -
crontab -l | grep pg_backup
```

---

## Step 5: Test Restore (Non-Destructive)

```bash
# Create throwaway test database
docker exec ${CONTAINER_NAME} psql -U ${DB_USER} -c "CREATE DATABASE ${DB_NAME}_restore_test;"

# Restore latest backup into it
LATEST=$(ls -t ${BACKUP_DIR}/${DB_NAME}_*.sql.gz | head -1)
gunzip -c "${LATEST}" | docker exec -i ${CONTAINER_NAME} psql -U ${DB_USER} -d ${DB_NAME}_restore_test

# Spot-check (adjust table names per service)
docker exec ${CONTAINER_NAME} psql -U ${DB_USER} -d ${DB_NAME}_restore_test -c "\dt" | head -20

# Cleanup
docker exec ${CONTAINER_NAME} psql -U ${DB_USER} -c "DROP DATABASE ${DB_NAME}_restore_test;"
```

---

## Emergency Restore

```bash
# 1. Stop the application container (not postgres)
docker stop <app-container>

# 2. Drop and recreate
docker exec ${CONTAINER_NAME} psql -U ${DB_USER} -c "DROP DATABASE ${DB_NAME};"
docker exec ${CONTAINER_NAME} psql -U ${DB_USER} -c "CREATE DATABASE ${DB_NAME} OWNER ${DB_USER};"

# 3. Restore
LATEST=$(ls -t ${BACKUP_DIR}/${DB_NAME}_*.sql.gz | head -1)
gunzip -c "${LATEST}" | docker exec -i ${CONTAINER_NAME} psql -U ${DB_USER} -d ${DB_NAME}

# 4. Restart app
docker start <app-container>
```

---

## Monitoring Hook (Optional)

Add to your monitoring stack:

```bash
LATEST_AGE=$(( $(date +%s) - $(stat -c %Y $(ls -t ${BACKUP_DIR}/${DB_NAME}_*.sql.gz | head -1)) ))
if [ ${LATEST_AGE} -gt 90000 ]; then
  echo "WARNING: Latest ${DB_NAME} backup is more than 25 hours old"
fi
```

---

## Checklist

```
□ Manual backup produces valid .sql.gz
□ Backup log shows success
□ Gzip integrity check passes
□ Cron job installed
□ Test restore succeeds
□ Test database cleaned up
```