docs: expand architecture documentation with scaling strategy, API surface reference, and video normalization spec

2026-08-04 20:57:33 +02:00
1 parent d4d7806189
commit 207401b5fb
@@ -311,7 +311,39 @@ Immutable segment naming + targeted Cloudflare Cache Rules + R2 ($0 egress) = ne

 ### Video Normalization & Playout

-All source assets must be pre-normalized (H.264/AVC, AAC-LC, constant 30 fps, 2s keyframe interval, CRF). Prevents glitches during continuous concat. FFmpeg `-c copy` preferred for efficiency.
+All source assets must be pre-normalized before they are accepted into production playlists. This prevents decode resets, timestamp drift, and audio/video discontinuities during continuous concat playout.
+
+#### Required Source Profile (Linear Void v1)
+
+| Field                   | Required Value                     | Notes                                                   |
+| ----------------------- | ---------------------------------- | ------------------------------------------------------- |
+| Container               | MP4                                | Single-video-asset input format                         |
+| Video codec             | H.264/AVC (`libx264`)              | Baseline delivery codec for broad compatibility         |
+| Audio codec             | AAC-LC                             | Stereo preferred                                        |
+| Resolution              | 1280x720 or 1920x1080              | Keep single resolution per playlist block when possible |
+| Framerate               | Constant 30 fps (`-r 30`)          | Variable frame rate content must be normalized          |
+| GOP / keyframe interval | 2 seconds (`-g 60 -keyint_min 60`) | Matches HLS segment boundaries better                   |
+| Pixel format            | `yuv420p`                          | Browser compatibility baseline                          |
+| Audio sample rate       | 48 kHz                             | Stable timing for concat playout                        |
+| Audio bitrate           | 128k-192k                          | Predictable quality envelope                            |
+
+#### Reference Normalization Command
+
+```bash
+ffmpeg -i input.mov \
+  -c:v libx264 -preset medium -crf 21 \
+  -r 30 -g 60 -keyint_min 60 -sc_threshold 0 \
+  -pix_fmt yuv420p \
+  -c:a aac -b:a 160k -ar 48000 -ac 2 \
+  -movflags +faststart \
+  output-normalized.mp4
+```
+
+#### Verification Gate (ffprobe)
+
+- Validate codec, fps, resolution, and keyframe cadence before upload acceptance.
+- Reject non-conforming files from admin ingest with actionable error feedback.
+- Keep verification logic aligned with runtime playout assumptions to preserve `-c copy` efficiency where possible.

 ### Monitoring & Resilience

@@ -366,6 +398,98 @@ Operational resilience baseline:
 - Weekly backup and restore drills for stateful data (`data/chat`, playlist metadata, Postgres).
 - Incident runbook with triage order: edge reachability -> origin health -> playout progression -> chat connectivity -> data-plane dependencies.

+### API Documentation Reference
+
+Linear Void currently exposes three operational API surfaces. The canonical detailed contract should live in `API.md`, while this section provides the architecture-level map.
+
+#### Chat WebSocket API
+
+- Endpoint: `/ws`
+- Transport: `wss://` in production, `ws://` locally
+- Query parameters:
+  - `username`
+  - `room`
+- Message envelope (typical):
+  - `room`
+  - `username`
+  - `text`
+  - `type` (`public`, `private`, `system`)
+- Responsibilities:
+  - room fan-out
+  - private DM channel routing
+  - moderation command handling
+  - rate limiting and presence integration
+
+#### Playout and Delivery REST API
+
+- Health endpoints:
+  - playout health (`/health` on playout service)
+  - edge/origin health (`/health` via nginx)
+- Stream delivery:
+  - HLS manifest and segment path namespace under `/hls/`
+- Responsibilities:
+  - expose liveness for orchestration and monitoring
+  - provide stable HLS path contract for viewer and CDN
+
+#### Admin REST API
+
+- Auth/session:
+  - `/api/admin/login`
+  - `/api/admin/logout`
+  - `/api/admin/session`
+- Operational/admin domains:
+  - overview, analytics, users, moderation, schedule, playlist, media
+- Media upload domain:
+  - `/api/admin/media/uploads` (init/resume)
+  - `/api/admin/media/uploads/{uploadId}/chunk`
+  - `/api/admin/media/uploads/{uploadId}/complete`
+- Responsibilities:
+  - protected control plane for operator workflows
+  - media metadata + upload orchestration
+  - moderation/audit and system status management
+
+### Cloudflare Configuration Reference
+
+Cloudflare is part of the production control plane, not only a CDN edge. The following configuration set is required to maintain cost, latency, and reliability targets.
+
+#### DNS and Zone Routing
+
+- `linearvoid.tv` -> application origin (nginx)
+- `www.linearvoid.tv` -> redirect to apex
+- `media.linearvoid.tv` -> media domain for HLS/object delivery when split-domain mode is enabled
+
+#### Cache Rules Baseline
+
+- HLS segments (`.ts`, `.m4s`):
+  - Cache Everything
+  - long TTL (immutable)
+  - respect immutable semantics
+- Manifests (`.m3u8`):
+  - short TTL (1-10s)
+  - revalidation-friendly policy for timeline freshness
+
+#### Edge Security and Controls
+
+- Enforce HTTPS/WSS and redirect HTTP to HTTPS.
+- Enable WAF baseline protections for common web exploits.
+- Apply rate limits for abusive request patterns (especially auth/admin paths).
+- Keep origin exposure minimized (prefer Cloudflare-only public ingress where feasible).
+
+#### Worker and Header Policy
+
+- Use Worker logic for immutable cache headers and request normalization where cache rules alone are insufficient.
+- Keep CORS behavior explicit for HLS resources to support browser playback.
+
+#### Operations and Validation
+
+- Validate cache behavior after deployment:
+  - expected cache status progression (MISS -> HIT)
+  - manifest freshness under active playout
+- Track edge metrics and adjust:
+  - cache hit ratio
+  - request volume and error rates
+  - ToS/cost posture for sustained traffic profiles
+
 ### Security & Moderation

 Security is split between edge controls (Cloudflare), reverse proxy controls (nginx), and application controls (chat/admin backend).
@@ -490,6 +614,41 @@ See **Quality Goals** table in the Introduction section. Primary scenarios focus
 - Trigger: origin CPU/memory pressure on playout host.
  - Action: optimize FFmpeg profile, isolate services, add secondary origin.

+### Scaling Strategy
+
+Scaling is designed to preserve cost efficiency first, then increase throughput and resilience in controlled phases.
+
+#### Phase 1: Vertical + Cache-First (Current Baseline)
+
+- Single primary origin in US-East with strong Cloudflare edge caching.
+- Optimize segment immutability and manifest TTL before adding infrastructure.
+- Scale compute vertically when CPU/memory pressure appears on playout/chat host.
+
+#### Phase 2: Service Separation
+
+- Split playout, chat, and observability workloads across dedicated nodes/VMs.
+- Isolate noisy workloads (analytics, heavy admin tasks) from latency-sensitive chat paths.
+- Introduce managed PostgreSQL/Redis or dedicated state nodes where operationally justified.
+
+#### Phase 3: Multi-Origin Resilience
+
+- Add warm standby or active-secondary origin.
+- Use health-aware DNS/origin failover strategy.
+- Keep HLS path and cache contract stable so viewer impact during failover is minimized.
+
+#### Phase 4: Regional and Throughput Expansion
+
+- Add additional origin region only when audience distribution and latency justify it.
+- Keep chat affinity strategy explicit (regional routing, state replication considerations).
+- Continuously evaluate cache miss economics vs additional origin complexity.
+
+#### Scaling Triggers
+
+- Rising cache miss ratio with sustained traffic growth.
+- Chat p95/p99 latency drift or websocket error growth.
+- Persistent origin resource saturation despite optimization.
+- Increased blast-radius concerns from single-host dependency.
+
 ### Disaster Recovery and Backup Procedures

 #### Recovery Targets