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

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

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

cloud-init integration

#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
007	postgres-admin-role	iwanhae OS user -> PG superuser (peer auth)

Roadmap

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