# Mini-PaaS Deployment System

## Overview

A pull-based deployment system that allows deploying Nix-built services without full NixOS rebuilds. Services are defined in a manifest, pulled from an S3 binary cache, and managed as systemd units with Caddy for reverse proxying.

## Problem Statement

Current deployment (`push.sh` + full NixOS rebuild) is slow and heavyweight:
- Every service change requires rebuilding the entire NixOS configuration
- Adding a new service requires modifying Biz.nix and doing a full rebuild
- Deploy time from "code ready" to "running in prod" is too long

## Goals

1. **Fast deploys**: Update a single service in <5 minutes without touching others
2. **Independent services**: Deploy services without NixOS rebuild
3. **Add services dynamically**: New services via manifest, no NixOS changes needed
4. **Maintain NixOS for base OS**: Keep NixOS for infra (Postgres, SSH, firewall)
5. **Clear scale-up path**: Single host now, easy migration to Nomad later

## Key Design Decisions

1. **Nix closures, not Docker**: Deploy Nix store paths directly, not containers. Simpler, no Docker daemon needed. Use systemd hardening for isolation.

2. **Pull-based, not push-based**: Target host polls S3 for manifest changes every 5 min. No SSH needed for deploys, just update manifest.

3. **Caddy, not nginx**: Caddy has admin API for dynamic route updates and automatic HTTPS. No config file regeneration needed.

4. **Separation of concerns**:
   - `bild`: Build tool, adds `--cache` flag to sign+push closures
   - `push.sh`: Deploy orchestrator, handles both NixOS and service deploys
   - `deployer`: Runs on target, polls manifest, manages services

5. **Out-of-band secrets**: Secrets stored in `/var/lib/biz-secrets/*.env`, manifest only references paths. No secrets in S3.

6. **Nix profiles for rollback**: Each service gets a Nix profile, enabling `nix-env --rollback`.

## Relevant Existing Files

- `Omni/Bild.hs` - Build tool, modify to add `--cache` flag
- `Omni/Bild.nix` - Nix build library, has `bild.run` for building packages
- `Omni/Ide/push.sh` - Current deploy script, enhance for service deploys
- `Biz.nix` - Current NixOS config for biz host
- `Biz/Packages.nix` - Builds all Biz packages
- `Biz/PodcastItLater/Web.nix` - Example NixOS service module (to be replaced)
- `Biz/PodcastItLater/Web.py` - Example Python service (deploy target)
- `Omni/Os/Base.nix` - Base NixOS config, add S3 substituter here

## Architecture

```
┌─────────────────────────────────────────────────────────────────────────────┐
│                              DEV MACHINE                                     │
│                                                                              │
│  ┌─────────────────────────────────────────────────────────────────────┐   │
│  │                           push.sh <target>                           │   │
│  │                                                                      │   │
│  │  if target.nix:     (NixOS deploy - existing behavior)              │   │
│  │    bild <target>                                                     │   │
│  │    nix copy --to ssh://host                                         │   │
│  │    ssh host switch-to-configuration                                 │   │
│  │                                                                      │   │
│  │  else:              (Service deploy - new behavior)                 │   │
│  │    bild <target> --cache  ──▶  sign + push closure to S3           │   │
│  │    update manifest.json in S3 with new storePath                    │   │
│  │    (deployer on target will pick up changes)                        │   │
│  └─────────────────────────────────────────────────────────────────────┘   │
│                                                                              │
│  Separation of concerns:                                                     │
│  - bild: Build + sign + push to S3 cache (--cache flag)                     │
│  - push.sh: Orchestrates deploy, updates manifest, handles both modes       │
└─────────────────────────────────────────────────────────────────────────────┘
                                      │
                                      ▼
┌─────────────────────────────────────────────────────────────────────────────┐
│                    DO SPACES (S3 BINARY CACHE) - PRIVATE                    │
│                                                                              │
│   /nar/*.nar.xz           ← Compressed Nix store paths                      │
│   /*.narinfo              ← Metadata + signatures                           │
│   /nix-cache-info         ← Cache metadata                                  │
│   /manifest.json          ← Current deployment state                        │
│   /manifests/             ← Historical manifests for rollback               │
│     manifest-<ts>.json                                                       │
│                                                                              │
│   Authentication: AWS credentials (Spaces access key)                       │
│   - Dev machine: write access for pushing                                   │
│   - Target host: read access for pulling                                    │
└─────────────────────────────────────────────────────────────────────────────┘
                                      │
                              poll every 5 min
                                      ▼
┌─────────────────────────────────────────────────────────────────────────────┐
│                              TARGET HOST (biz)                              │
│                                                                              │
│  ┌──────────────────────────────────────────────────────────────────────┐  │
│  │                         biz-deployer                                  │  │
│  │  (Python systemd service, runs every 5 min via timer)                │  │
│  │                                                                       │  │
│  │  1. Fetch manifest.json from S3                                      │  │
│  │  2. Compare to local state                                           │  │
│  │  3. For changed services:                                            │  │
│  │     - nix copy --from s3://... <storePath>                          │  │
│  │     - Generate systemd unit file                                     │  │
│  │     - Create GC root                                                 │  │
│  │     - systemctl daemon-reload && restart                            │  │
│  │  4. Update Caddy routes via API                                      │  │
│  │  5. Save local state                                                 │  │
│  └──────────────────────────────────────────────────────────────────────┘  │
│                                                                              │
│  Directories:                                                                │
│  - /var/lib/biz-deployer/services/*.service  (generated units)             │
│  - /var/lib/biz-deployer/state.json          (local state)                 │
│  - /var/lib/biz-secrets/*.env                (secret env files)            │
│  - /nix/var/nix/gcroots/biz/*                (GC roots)                    │
│                                                                              │
│  NixOS manages:                                                              │
│  - Base OS, SSH, firewall                                                   │
│  - Caddy with admin API enabled                                             │
│  - PostgreSQL, Redis (infra services)                                       │
│  - biz-deployer service itself                                              │
└─────────────────────────────────────────────────────────────────────────────┘
```

## Components

### 1. S3 Binary Cache (DO Spaces)

**Bucket**: `omni-nix-cache` (private)
**Region**: `nyc3` (or nearest)

**Credentials**:
- Dev machine: `~/.aws/credentials` with `[digitalocean]` profile
- Target host: `/root/.aws/credentials` with same profile

**Signing key**:
- Generate: `nix-store --generate-binary-cache-key omni-cache cache-priv-key.pem cache-pub-key.pem`
- Private key: `~/.config/nix/cache-priv-key.pem` (dev machine only)
- Public key: Added to target's `nix.settings.trusted-public-keys`

**S3 URL format**:
```
s3://omni-nix-cache?profile=digitalocean&scheme=https&endpoint=nyc3.digitaloceanspaces.com
```

### 2. Manifest Schema (v1)

```json
{
  "version": 1,
  "generation": "2025-01-15T12:34:56Z",
  "services": [
    {
      "name": "podcastitlater-web",
      "artifact": {
        "type": "nix-closure",
        "storePath": "/nix/store/abc123-podcastitlater-web-1.2.3"
      },
      "hosts": ["biz"],
      "exec": {
        "command": "podcastitlater-web",
        "user": "pil-web",
        "group": "pil"
      },
      "env": {
        "PORT": "8000",
        "AREA": "Live",
        "DATA_DIR": "/var/podcastitlater",
        "BASE_URL": "https://podcastitlater.com"
      },
      "envFile": "/var/lib/biz-secrets/podcastitlater-web.env",
      "http": {
        "domain": "podcastitlater.com",
        "path": "/",
        "internalPort": 8000
      },
      "systemd": {
        "after": ["network-online.target", "postgresql.service"],
        "requires": [],
        "restart": "on-failure",
        "restartSec": 5
      },
      "hardening": {
        "dynamicUser": false,
        "privateTmp": true,
        "protectSystem": "strict",
        "protectHome": true
      },
      "revision": "abc123def"
    }
  ]
}
```

### 3. Deployer Service (Omni/Deploy/Deployer.py)

Python service that:
- Polls manifest from S3
- Pulls Nix closures
- Generates systemd units
- Updates Caddy via API
- Manages GC roots
- Tracks local state

### 4. NixOS Module (Omni/Deploy/Deployer.nix)

Configures:
- biz-deployer systemd service + timer
- Caddy with admin API
- S3 substituter configuration
- Required directories and permissions

### 5. Bild Integration (Omni/Bild.hs)

New `--cache` flag that:
1. Builds the target
2. Signs the closure with cache key (using NIX_CACHE_KEY env var)
3. Pushes to S3 cache
4. Outputs the store path for push.sh to use

Does NOT update manifest - that's push.sh's responsibility.

### 6. Push.sh Enhancement (Omni/Ide/push.sh)

Detect deploy mode from target extension:
- `.nix` → NixOS deploy (existing behavior)
- `.py`, `.hs`, etc. → Service deploy (new behavior)

For service deploys:
1. Call `bild <target> --cache`
2. Capture store path from bild output
3. Fetch current manifest.json from S3
4. Archive current manifest to manifests/manifest-<timestamp>.json
5. Update manifest with new storePath for this service
6. Upload new manifest.json to S3
7. Deployer on target picks up change within 5 minutes

## Migration Path

### Phase 1: Infrastructure Setup
1. Create DO Spaces bucket
2. Generate signing keys
3. Configure S3 substituter on target
4. Deploy base deployer service (empty manifest)

### Phase 2: Migrate First Service
1. Choose non-critical service (e.g., podcastitlater-worker)
2. Add to manifest with different port
3. Verify via staging route
4. Flip Caddy to new service
5. Disable old NixOS-managed service

### Phase 3: Migrate Remaining Services
- Repeat Phase 2 for each service
- Order: worker → web → storybook

### Phase 4: Cleanup
- Remove service-specific NixOS modules
- Simplify Biz.nix to base OS only

## Rollback Strategy

1. Each deploy archives current manifest to `/manifests/manifest-<ts>.json`
2. Rollback = copy old manifest back to `manifest.json`
3. Deployer sees new generation, converges to old state
4. GC roots keep old closures alive (last 5 versions per service)

## Scale-up Path

| Stage | Hosts | Changes |
|-------|-------|---------|
| Current | 1 | Full architecture as described |
| 2-3 hosts | 2-3 | Add `hosts` filtering, each host runs deployer |
| 4+ hosts | 4+ | Consider Nomad with nix-nomad for job definitions |

## Security Considerations

- S3 bucket is private (authenticated reads/writes)
- Signing key never leaves dev machine
- Secrets stored out-of-band in `/var/lib/biz-secrets/`
- systemd hardening for service isolation
- Deployer validates manifest schema before applying

## File Locations

```
Omni/
  Deploy/
    PLAN.md              # This document
    Deployer.py          # Main deployer service
    Deployer.nix         # NixOS module
    Manifest.py          # Manifest schema/validation
    Systemd.py           # Unit file generation
    Caddy.py             # Caddy API integration
    S3.py                # S3 operations (for deployer)
  Bild.hs                # Add --cache flag for sign+push
  Ide/
    push.sh              # Enhanced: NixOS deploy OR service deploy + manifest update
```