Add PostgreSQL with automated hot backup setup

Weekly full backups via pg_basebackup and continuous WAL archiving
for point-in-time recovery, running as Docker Compose services.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitignore

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+.env

README.md

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+# PostgreSQL with Hot Backup
+
+PostgreSQL 18 with automated weekly full backups and continuous WAL archiving for point-in-time recovery.
+
+## Services
+
+| Service | Description |
+|---------|-------------|
+| `postgres-db` | PostgreSQL 18 with WAL archiving enabled |
+| `postgres-backup` | Sidecar that runs weekly full backups via `pg_basebackup` |
+
+## Quick Start
+
+```bash
+cp .env.example .env  # edit with your credentials
+docker compose up -d
+```
+
+## Configuration
+
+Environment variables in `.env`:
+
+| Variable | Description | Default |
+|----------|-------------|---------|
+| `POSTGRES_USER` | Database user | `postgres` |
+| `POSTGRES_PASSWORD` | Database password | — |
+| `POSTGRES_DB` | Default database name | `postgres` |
+| `PGPORT` | Host port for PostgreSQL | `5432` |
+
+## Backup Strategy
+
+### Full Backups (Weekly)
+- `pg_basebackup` runs on startup, then every 7 days
+- Stored in `/data/backup/postgres/full/full_<timestamp>/`
+- Hot backup — no downtime required
+
+### Incremental via WAL Archiving (Continuous)
+- PostgreSQL archives Write-Ahead Log segments as they complete (~16MB each)
+- Stored in `/data/backup/postgres/wal/`
+- Captures every transaction between full backups
+
+### Backup Location
+
+```
+/data/backup/postgres/
+├── full/
+│   └── full_2026-03-06_12-00-00/   # weekly full snapshots
+└── wal/
+    ├── 000000010000000000000001      # archived WAL segments
+    └── ...
+```
+
+## Restore
+
+To perform point-in-time recovery:
+
+1. Stop PostgreSQL
+2. Replace the data directory with a full backup:
+   ```bash
+   cp -r /data/backup/postgres/full/full_<timestamp>/ /path/to/pgdata/
+   ```
+3. Create a `recovery.signal` file in the data directory
+4. Configure `restore_command` in `postgresql.conf`:
+   ```
+   restore_command = 'cp /data/backup/postgres/wal/%f %p'
+   ```
+5. Optionally set `recovery_target_time` for a specific point in time:
+   ```
+   recovery_target_time = '2026-03-06 14:30:00'
+   ```
+6. Start PostgreSQL — it will replay WAL files and recover
+
+## Monitoring
+
+```bash
+# Check backup service logs
+docker compose logs postgres-backup
+
+# Check WAL archiving activity
+docker compose logs postgres-db | grep archive
+
+# List full backups
+ls /data/backup/postgres/full/
+
+# List archived WAL files
+ls /data/backup/postgres/wal/
+```
+
+## Volumes
+
+| Volume/Mount | Purpose |
+|-------------|---------|
+| `postgres_data` (Docker volume) | PostgreSQL data directory |
+| `/data/backup/postgres/wal` | Archived WAL segments |
+| `/data/backup/postgres` | All backups (full + WAL) |

docker-compose.yml

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+
+services:
+  postgres-db:
+    image: postgres:18
+    container_name: postgres-db
+    restart: unless-stopped
+    environment:
+      POSTGRES_USER: ${POSTGRES_USER}
+      POSTGRES_PASSWORD: ${POSTGRES_PASSWORD}
+      POSTGRES_DB: ${POSTGRES_DB}
+    ports:
+      - "${PGPORT}:5432"
+    volumes:
+      - postgres_data:/var/lib/postgresql
+      - /data/backup/postgres/wal:/backup/wal
+      - ./init-replication-hba.sh:/docker-entrypoint-initdb.d/init-replication-hba.sh:ro
+    command:
+      - postgres
+      - -c
+      - wal_level=replica
+      - -c
+      - archive_mode=on
+      - -c
+      - archive_command=test ! -f /backup/wal/%f && cp %p /backup/wal/%f
+
+  postgres-backup:
+    image: postgres:18
+    container_name: postgres-backup
+    restart: unless-stopped
+    depends_on:
+      - postgres-db
+    environment:
+      POSTGRES_USER: ${POSTGRES_USER}
+      PGPASSWORD: ${POSTGRES_PASSWORD}
+    volumes:
+      - /data/backup/postgres:/backup
+    entrypoint: ["/bin/bash", "-c"]
+    command:
+      - |
+        mkdir -p /backup/wal /backup/full
+        while true; do
+          STAMP=$$(date +%Y-%m-%d_%H-%M-%S)
+          echo "Starting full backup: full_$$STAMP"
+          pg_basebackup -h postgres-db -U "$$POSTGRES_USER" -D "/backup/full/full_$$STAMP" -Fp -Xs -P
+          echo "Full backup complete: full_$$STAMP"
+          sleep 604800
+        done
+
+volumes:
+  postgres_data:

init-replication-hba.sh

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+#!/bin/bash
+# Allow replication connections from the Docker network
+echo "host replication all all scram-sha-256" >> "$PGDATA/pg_hba.conf"