sneak
83bd23945c
Reorder host list: datavi.be first, then LLM APIs, then cloud providers (AWS, GCP, Azure), then CDN/hosting, then GitHub.
143 lines
4.4 KiB
Markdown
143 lines
4.4 KiB
Markdown
NetWatch is an MIT-licensed JavaScript single-page application by
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[@sneak](https://sneak.berlin) that provides real-time network latency
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monitoring to common internet hosts, displayed with color-coded figures and
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sparkline graphs, served from a static bucket or Docker container.
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## Getting Started
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```bash
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# Install dependencies
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yarn install
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# Development server
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yarn dev
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# Production build
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yarn build
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# Preview production build
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yarn preview
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# Docker
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docker build -t netwatch .
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docker run -p 8080:8080 netwatch
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```
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## Rationale
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When debugging network issues, it's useful to have a persistent at-a-glance view
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of latency and reachability to multiple well-known internet endpoints. NetWatch
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provides this as a zero-dependency SPA that can be deployed anywhere static
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files are served, with no backend required.
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## Design
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The application is a single-page app built with Vite and Tailwind CSS v4. All
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code lives in `src/main.js` with a class-based architecture:
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- **`CONFIG`**: Frozen configuration object (update interval, timeouts, axis
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ticks, etc.)
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- **`HostState`**: Per-host state management — history buffer, latency tracking,
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status transitions
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- **`AppState`**: Top-level state container — WAN hosts, local hosts, pause
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state, aggregate stats
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- **`SparklineRenderer`**: Canvas 2D sparkline drawing with fixed axes,
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color-coded line segments, error regions, and DPR-aware scaling
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- **UI functions**: `buildUI()` constructs the DOM, `updateHostRow()` /
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`updateSummary()` / `updateHealthBox()` handle incremental updates
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- **`tick()`**: Main loop — measures all hosts in parallel via `Promise.all`,
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pushes samples, redraws UI. When paused, pushes blank markers (no probes, no
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false outage)
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### Monitoring targets
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- **11 WAN hosts**: datavi.be, Anthropic API, OpenAI API, AWS, GCP, Azure,
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DigitalOcean, Cloudflare, Fastly, Akamai, GitHub
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- **1 Local host**: Local Gateway (192.168.100.1), tracked separately from WAN
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stats
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### Latency measurement
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HEAD requests with `mode: 'no-cors'` and `cache: 'no-store'`, timed with
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`performance.now()`. 1-second timeout; anything over 1000ms is clamped to
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unreachable. IPv4 only.
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### Color coding
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| Latency | Color |
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| ----------- | ------ |
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| < 50ms | Green |
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| < 100ms | Lime |
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| < 200ms | Yellow |
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| < 500ms | Orange |
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| >= 500ms | Red |
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| Unreachable | Gray |
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### Output structure
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```
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dist/
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├── index.html
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└── assets/
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├── index-*.css
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└── index-*.js
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```
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## Features
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- Real-time monitoring with 2s update interval and 300s history sparklines
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- Health indicator: green (HEALTHY) or red (DEGRADED) based on WAN reachability
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- Summary stats: reachable count, min/max/avg latency across WAN hosts only
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- Fixed chart axes: Y-axis 0–1000ms, X-axis 0–300s
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- Color-coded latency figures and sparkline line segments
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- Play/pause: pause stops probes but history keeps scrolling (blank gaps, no
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false outage)
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- Clickable service URLs
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- Canvas-based sparkline rendering with devicePixelRatio scaling
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- Zero runtime dependencies: all resources bundled into build artifacts
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## Deployment
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After running `yarn build`, deploy the contents of the `dist/` directory to any
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static file host (S3, GCS, Cloudflare Pages, Vercel, Netlify, GitHub Pages) or
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use the Docker image behind a reverse proxy.
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The Docker image:
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- Listens on port 8080 by default (override with `PORT` env var)
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- Trusts `X-Forwarded-For` from RFC1918 reverse proxies (10/8, 172.16/12,
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192.168/16)
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- Sends access logs to stdout
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- Caches static assets with immutable headers
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## Browser Compatibility
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Requires a modern browser with ES modules, Fetch API, Canvas API, and CSS custom
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properties.
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## Limitations
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- **CORS**: Some hosts may block cross-origin HEAD requests. The app uses
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`no-cors` mode which allows the request but provides opaque responses. Latency
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is still measurable based on request timing.
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- **Local gateway**: The 192.168.100.1 endpoint requires the host to be
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accessible from your network.
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- **Network conditions**: Measurements reflect browser-to-endpoint latency,
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which includes your local network, ISP, and internet routing.
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## TODO
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- Add unit tests
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- Add eslint for JS linting (currently lint target runs prettier only)
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- Add configurable host list (environment variable or config file)
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- Add latency history export (CSV/JSON)
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- Add notification/alert when status changes to DEGRADED
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## License
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MIT. See [LICENSE](LICENSE).
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## Author
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[@sneak](https://sneak.berlin)
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