# sysmig

Lightweight tool that manages host state in DB-migration (Flyway) style.
Started for a 1GB VM (`ocrt-postgres`), but deployable to any machine
via cloud-init.

## Usage

```bash
sudo bash /opt/sysmig/sysmig up        # apply all pending migrations (idempotent)
sudo bash /opt/sysmig/sysmig down      # roll back the last migration
sudo bash /opt/sysmig/sysmig down all  # roll back everything (reverse order)
bash /opt/sysmig/sysmig status         # show status (no root required)
```

- Migrations: `migrations/NNN-name.sh`, receiving `up`/`down` as `$1`
- Applied history: `/var/lib/sysmig/applied` - applied entries never re-run
- On failure the run aborts at that step; earlier steps stay applied

## Adding a new migration

1. Create `migrations/NNN-name.sh` (number higher than existing; leave gaps)
2. Implement both `up` and `down` cases - both must actually work
3. Commit & push, then on the server: `git pull && sudo bash sysmig/sysmig up`

## cloud-init integration

```yaml
#cloud-config
runcmd:
  - [ git, clone, <REPO_URL>, /opt/sysmig ]
  - [ bash, /opt/sysmig/sysmig, up ]
```

For a private repo you need an auth strategy:
- **deploy key** (existing machines): register a read-only key on the repo
- **fleet rollout**: make the repo public, or embed a read-only token in
  the https URL

## Current migrations

| #  | name                       | effect                                        |
|----|----------------------------|-----------------------------------------------|
| 001 | create-swap                | 2GB swap + fstab + vm.swappiness=10           |
| 002 | disable-networkd-dispatcher| reclaim ~27MB RAM                             |
| 003 | purge-exim4                | reclaim ~21MB RAM (package removed)           |
| 004 | purge-haveged              | reclaim ~8MB RAM (package removed)            |
| 005 | mount-pgdata               | /dev/sdb (20G) -> /var/lib/postgresql, fstab  |
| 006 | install-postgres           | PG 18 via PGDG repo, cluster on the disk     |

## Roadmap

- `010-tune-postgres` - 1GB tuning (shared_buffers=128MB, work_mem=4MB,
  max_connections=30, ...)