wan
08c585d048
Serverless clients -> many short connections, few TPS. pool_mode= transaction, max_client_conn=300, default_pool_size=20 (+reserve 5) matching max_connections=30. max_prepared_statements=200 for ORM prepared statements. localhost-only until remote-access migration (roadmap 015). README table + notes updated.
74 lines
3.3 KiB
Markdown
74 lines
3.3 KiB
Markdown
# sysmig
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Lightweight tool that manages host state in DB-migration (Flyway) style.
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Started for a 1GB VM (`ocrt-postgres`), but deployable to any machine
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via cloud-init.
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## Usage
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```bash
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sudo bash /opt/sysmig/sysmig up # apply all pending migrations (idempotent)
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sudo bash /opt/sysmig/sysmig down # roll back the last migration
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sudo bash /opt/sysmig/sysmig down all # roll back everything (reverse order)
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bash /opt/sysmig/sysmig status # history + drift check (exit 1 on drift)
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```
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- Migrations: `migrations/NNN-name.sh`, receiving `up`/`down`/`status` as `$1`
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- Applied history: `/var/lib/sysmig/applied` - applied entries never re-run
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- On failure the run aborts at that step; earlier steps stay applied
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- `status` runs each applied migration's read-only drift check (exit 1 on
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drift); DB checks need root, otherwise shown as `?`
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## Adding a new migration
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1. Create `migrations/NNN-name.sh` (number higher than existing; leave gaps)
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2. Implement `up`, `down` and `status` cases - up/down must actually work;
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`status` is a read-only check (exit 0 OK / 1 DRIFT / 2 unknown)
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3. Commit & push, then on the server: `git pull && sudo bash sysmig/sysmig up`
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## cloud-init integration
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```yaml
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#cloud-config
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runcmd:
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- [ git, clone, <REPO_URL>, /opt/sysmig ]
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- [ bash, /opt/sysmig/sysmig, up ]
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```
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For a private repo you need an auth strategy:
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- **deploy key** (existing machines): register a read-only key on the repo
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- **fleet rollout**: make the repo public, or embed a read-only token in
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the https URL
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## Current migrations
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| # | name | effect |
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|----|----------------------------|-----------------------------------------------|
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| 001 | create-swap | 2GB swap + fstab + vm.swappiness=10 |
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| 002 | disable-networkd-dispatcher| reclaim ~27MB RAM |
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| 003 | purge-exim4 | reclaim ~21MB RAM (package removed) |
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| 004 | purge-haveged | reclaim ~8MB RAM (package removed) |
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| 005 | mount-pgdata | /dev/sdb (20G) -> /var/lib/postgresql, fstab |
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| 006 | install-postgres | PG 18 via PGDG repo, cluster on the disk |
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| 007 | postgres-admin-role | iwanhae OS user -> PG superuser (peer auth) |
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| 008 | create-db-iwanhae | database `iwanhae` owned by admin role |
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| 010 | tune-postgres | 1GB stability: conns=30, cache hint, timeouts, temp_file_limit |
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| 011 | postgres-observability | pg_stat_statements, slow-log 500ms, io timing |
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| 012 | tune-cpu | parallel caps + jit=off for shared 2 vCPU |
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| 013 | install-pgbouncer | :6432 transaction pooling, localhost-only |
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## PgBouncer notes (013)
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Serverless clients (many connections, few TPS) connect to PgBouncer
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(`127.0.0.1:6432`, transaction mode) which opens at most ~25 real
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PostgreSQL backends - matching `max_connections=30` from 010 with room
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for admin sessions. Remote access is deliberately not opened yet; when
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it is: create an app role with a SCRAM password, export its verifier into
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`/etc/pgbouncer/userlist.txt` (snippet in 013's header), flip
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`listen_addr` and open the firewall.
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## Roadmap
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- `015-remote-access` - app role + SCRAM credentials, pgbouncer
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`listen_addr` + userlist.txt, pg_hba for the app CIDR, TLS, firewall
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