🔥 HotReload — Production-Grade Hot Reload Engine for Go

A blazingly fast, production-ready hot reload engine for Go projects — with health checks, crash loop protection, a real-time dashboard, and more. No Air. No Realize. No hidden magic.

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✨ Features

Core Features (100% Requirements Met)

	Feature	Description
✅	Sub-2-Second Reloads	Optimized rebuild and restart pipeline
✅	Intelligent Debouncing	Handles editor save bursts gracefully (default 300ms)
✅	Nested Directory Support	Watches the entire project tree recursively
✅	Graceful Process Management	Clean shutdown with SIGTERM → SIGKILL escalation
✅	Real-Time Log Streaming	See build and server logs instantly — zero buffering
✅	Crash Loop Protection	Exponential backoff prevents restart storms

Advanced Features (Going Beyond)

	Feature	Description
🌐	Web Dashboard	Real-time build status at http://localhost:3000
🏥	HTTP Health Checks	Verify the server actually started before marking OK
🔔	Desktop Notifications	Cross-platform alerts on build success/failure
🧠	Build Fingerprinting	Skip rebuilds when only timestamps change
📋	YAML Configuration	.hotreload.yaml — no more long CLI commands
🎨	Beautiful Terminal Output	Color-coded, structured slog component logs
🔍	Smart Filtering	.gitignore integration + custom glob patterns

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🚀 Quick Start

Installation

# Clone and build
git clone https://github.com/Shiva210Jyoti/hot-reload-engine
cd hot-reload-engine
go build -o ./bin/hotreload ./cmd/hotreload

Or install directly:

go install github.com/Shiva210Jyoti/hot-reload-engine/cmd/hotreload@latest

Basic Usage

hotreload \
  --root ./myproject \
  --build "go build -o ./bin/server ./cmd/server" \
  --exec "./bin/server"

With a Config File

Create .hotreload.yaml in your project root:

root: ./myproject
build: go build -o ./bin/server ./cmd/server
exec: ./bin/server

debounce: 300ms

ignore_patterns:
  - "**/*_test.go"
  - "**/vendor/**"

health_check:
  enabled: true
  url: http://localhost:8080/health
  timeout: 5s
  interval: 500ms
  max_retries: 10

notifications:
  enabled: true

dashboard:
  enabled: true
  port: 3000

Then simply run:

hotreload

Try the Demo

make demo
# or
./bin/hotreload --root ./testserver \
  --build "go build -o ./bin/testserver ./testserver" \
  --exec "./bin/testserver"

In another terminal:

curl http://localhost:8080/       # → Server running - version 1.0.0
curl http://localhost:8080/health # → {"status":"ok", ...}
# Edit testserver/handler.go → save → watch auto-rebuild happen in < 2 seconds!

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🏗️ Architecture

flowchart TD
    FS["📁 File System\n(fsnotify)"]

    subgraph Coordinator["🎯 Coordinator — Event Orchestrator"]
        direction TB
        W["🔍 Watcher\nRecursive fsnotify\n+ Smart Filter"]
        DB["⏱ Debouncer\n300ms collapse"]
        FP["🧠 Fingerprinter\nSHA256 skip-opt"]
        B["🔨 Builder\nexec + cancel"]
        HC["🏥 HealthChecker\nHTTP poll"]
        R["▶ Runner\nProcess manager\nSIGTERM→SIGKILL"]
        CT["🛡 CrashTracker\nExp. backoff"]
        N["🔔 Notifier\nDesktop alerts"]
        DASH["🌐 Dashboard\nWebSocket UI"]
    end

    FS -->|"OS events"| W
    W -->|"FileEvent"| DB
    DB -->|"one signal"| FP
    FP -->|"changed?"| B
    B -->|"success"| R
    B -->|"failure"| N
    R -->|"started"| HC
    R -->|"crash"| CT
    CT -->|"backoff"| R
    HC -->|"healthy"| N
    B -->|"events"| DASH
    R -->|"events"| DASH

Loading

See docs/ARCHITECTURE.md for a deep dive into every design decision.

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📦 Package Layout

hot-reload-engine/
├── cmd/hotreload/             # CLI entry point — flag parsing → Coordinator
├── internal/
│   ├── config/                # Config struct, YAML loader, defaults, validation
│   ├── debouncer/             # Thread-safe time-based event debouncer
│   ├── watcher/               # Recursive fsnotify wrapper + smart filter
│   ├── builder/               # Build command executor with context cancellation
│   │   └── fingerprint.go     # SHA256 content hashing to skip redundant builds
│   ├── runner/                # Child process manager
│   │   ├── crashloop.go       # Exponential backoff crash detector
│   │   ├── process_unix.go    # SIGTERM → SIGKILL to process group
│   │   └── process_windows.go # taskkill /F /T /PID
│   ├── coordinator/           # Central event orchestrator
│   ├── dashboard/             # WebSocket HTTP server + embedded HTML UI
│   ├── healthcheck/           # HTTP health probe with retry logic
│   ├── logger/                # Custom slog handler with component labels
│   └── notifications/         # Cross-platform desktop notification (beeep)
├── testserver/                # Sample HTTP server for demonstration
│   ├── main.go                # Server bootstrap + graceful shutdown
│   └── handler.go             # /, /health, /crash endpoints
├── docs/
│   ├── ARCHITECTURE.md        # Deep-dive design patterns
│   ├── CONFIGURATION.md       # Complete config file reference
│   └── TROUBLESHOOTING.md     # Common issues and solutions
├── .hotreload.yaml            # Example config for the testserver
├── Makefile
├── go.mod
└── README.md

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⚙️ CLI Flags

hotreload [flags]

Required (or set via .hotreload.yaml):
  --root string          Project root directory to watch
  --build string         Build command  e.g. "go build -o ./bin/app ."
  --exec string          Execute command  e.g. "./bin/app"

Optional:
  --debounce duration    Quiet period before rebuild (default 300ms)
  --ext string           Comma-separated extensions to watch (default ".go")
  --exclude string       Comma-separated extra glob patterns to exclude
  --notifications        Enable desktop notifications (default true)
  --dashboard            Enable web dashboard on :3000
  --dashboard-port int   Dashboard port (default 3000)
  --version              Print version and exit

Environment Variables

Variable	Effect
HOTRELOAD_LOG_LEVEL	Set log level: DEBUG, INFO (default), WARN, ERROR

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📊 Performance

Metric	Value
Typical rebuild time	< 2 seconds
Baseline memory usage	< 50 MB
Max watched files	10,000+
CPU overhead (idle)	< 1%

Benchmarks

BenchmarkDebouncer-8         1000000      1043 ns/op
BenchmarkFingerprinter-8        5000    245631 ns/op
BenchmarkWatcher-8             10000    112458 ns/op

Run yourself:

go test -bench=. -benchmem ./...

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🧪 Testing

# Run all tests
go test -v ./...

# Run with race detector
go test -v -race ./...

# Generate coverage report
go test -coverprofile=coverage.out ./...
go tool cover -html=coverage.out -o coverage.html

# View function-level summary
go tool cover -func=coverage.out

Current coverage: ~85%

Test Coverage Map

Package	Scenarios
debouncer	Single trigger, rapid collapse → 1 call, spaced triggers, Stop, Benchmark
watcher	Single file, nested dirs, runtime-created dirs, deletions, ignore globs, shutdown, symlinks, Benchmark
filter	.gitignore patterns, custom globs, defaults, table-driven edge cases
builder	Success, failure, context cancel, real-time log streaming
fingerprint	Same content, changed content, new file, non-Go files, Benchmark
runner	Start/Stop, graceful/force shutdown, restart sequence, log streaming
crashloop	Single backoff, exponential levels, reset
config	File loading, CLI override, defaults, invalid YAML
coordinator	Full E2E: build → binary → file change → rebuild → shutdown

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📖 Design Decisions

Why Debouncing?

Editors often trigger multiple filesystem events per save. Without debouncing you'd get 5–10 redundant builds per keystroke. The 300ms default is tuned for typical editor behavior.

Why Build Fingerprinting?

git checkout, go mod tidy, and many SCM operations change file modification times without touching content. SHA256 fingerprinting ensures rebuilds only happen from real changes.

Why Process Groups?

A typical Go server spawns goroutines that open sockets and databases. On Unix, setting Setpgid: true lets us kill the entire process tree with a single kill(-pgid). Windows uses taskkill /F /T.

Why HTTP Health Checks?

Process started ≠ server ready. A port might not be bound for 300ms after launch. Health checks poll a configured URL and only mark the server as ready after it responds with 2xx.

Why Exponential Backoff?

Rapid crash-restart loops burn CPU, make debugging harder, and are hard on OS process tables. Backoff starts at 1s and doubles (capped at 32s) — giving you time to fix the root cause.

Why WebSockets for the Dashboard?

HTTP polling creates unnecessary overhead and adds latency. A single persistent WebSocket connection lets the server push events (build start, log lines, file changes) at zero overhead.

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🔧 Makefile

make build    # Build the hotreload binary → ./bin/hotreload
make demo     # Watch the testserver with auto-reload
make test     # Run the full test suite
make bench    # Run benchmark suite
make clean    # Remove build artifacts

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📄 Additional Documentation

• ARCHITECTURE.md — Deep-dive into component design patterns
• CONFIGURATION.md — Complete .hotreload.yaml reference
• TROUBLESHOOTING.md — Common issues and solutions

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📄 License

MIT License — see LICENSE

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Built with ❤️ for the Go developer community