Health Check Generator

Creates Health Check infrastructure for monitoring application and dependency health.

When to Use

Scenario	Example
Load balancer routing	Kubernetes liveness/readiness probes
Monitoring	Prometheus health scraping
Deployment readiness	Verify all dependencies before serving traffic
Dependency status	Check Database, Redis, RabbitMQ availability

Component Characteristics

HealthCheckInterface

• name(): string — unique identifier for the check
• check(): HealthCheckResult — execute the health check

HealthStatus Enum

• Healthy: All systems operational
• Degraded: Partially operational, non-critical issues
• Unhealthy: System is down or critical failure

HealthCheckResult

• Immutable value object
• Properties: name, status (HealthStatus), durationMs (float), details (array)
• Static factory methods: healthy(), unhealthy(), degraded()

HealthCheckRunner

• Accepts iterable of HealthCheckInterface implementations
• Runs all checks with configurable timeout
• Aggregates overall status (worst status wins)
• Catches exceptions as unhealthy results

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Generation Process

Step 1: Generate Domain Components

Path: src/Domain/Shared/Health/

1. HealthCheckInterface.php — Interface for health checks
2. HealthStatus.php — Enum with Healthy/Degraded/Unhealthy states
3. HealthCheckResult.php — Immutable result value object

Step 2: Generate Infrastructure Checkers

Path: src/Infrastructure/Health/

1. DatabaseHealthCheck.php — PDO connectivity check
2. RedisHealthCheck.php — Redis connectivity check
3. RabbitMqHealthCheck.php — RabbitMQ connectivity check
4. HealthCheckRunner.php — Runs all checks and aggregates status

Step 3: Generate Presentation Endpoint

Path: src/Presentation/Api/Action/

1. HealthCheckAction.php — PSR-15 handler returning JSON response

Step 4: Generate Tests

1. HealthCheckResultTest.php — Result construction and serialization
2. HealthCheckRunnerTest.php — Aggregation and error handling
3. HealthCheckActionTest.php — HTTP response codes and format

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File Placement

Component	Path
Domain Interfaces & VOs	src/Domain/Shared/Health/
Infrastructure Checkers	src/Infrastructure/Health/
Presentation Action	src/Presentation/Api/Action/
Unit Tests (Domain)	tests/Unit/Domain/Shared/Health/
Unit Tests (Infra)	tests/Unit/Infrastructure/Health/
Unit Tests (Presentation)	tests/Unit/Presentation/Api/Action/

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Naming Conventions

Component	Pattern	Example
Interface	HealthCheckInterface	HealthCheckInterface
Status Enum	HealthStatus	HealthStatus
Result VO	HealthCheckResult	HealthCheckResult
Checker	{Service}HealthCheck	DatabaseHealthCheck
Runner	HealthCheckRunner	HealthCheckRunner
Action	HealthCheckAction	HealthCheckAction
Test	{ClassName}Test	HealthCheckResultTest

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Quick Template Reference

HealthCheckInterface

interface HealthCheckInterface
{
    public function name(): string;
    public function check(): HealthCheckResult;
}

HealthStatus

enum HealthStatus: string
{
    case Healthy = 'healthy';
    case Degraded = 'degraded';
    case Unhealthy = 'unhealthy';

    public function isOperational(): bool;
    public function merge(self $other): self;
}

HealthCheckResult

final readonly class HealthCheckResult
{
    public function __construct(
        public string $name,
        public HealthStatus $status,
        public float $durationMs,
        public array $details = []
    ) {}

    public static function healthy(string $name, float $durationMs): self;
    public static function unhealthy(string $name, float $durationMs, string $error): self;
    public static function degraded(string $name, float $durationMs, string $reason): self;
    public function toArray(): array;
}

---

Usage Example

// GET /health
$runner = new HealthCheckRunner($checkers, timeoutSeconds: 5);
$result = $runner->run();
// $result['status'] is HealthStatus, $result['checks'] is array<string, HealthCheckResult>

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Response Format (RFC Health Check JSON)

{
    "status": "healthy",
    "checks": {
        "database": {
            "name": "database",
            "status": "healthy",
            "duration_ms": 1.23,
            "details": {}
        },
        "redis": {
            "name": "redis",
            "status": "healthy",
            "duration_ms": 0.45,
            "details": {}
        },
        "rabbitmq": {
            "name": "rabbitmq",
            "status": "degraded",
            "duration_ms": 15.7,
            "details": {
                "reason": "High latency detected"
            }
        }
    }
}

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Anti-patterns to Avoid

Anti-pattern	Problem	Solution
Slow checks	Health endpoint times out	Set per-check timeouts
No timeouts	Single check blocks entire response	Use configurable timeout per runner
Exposing internals	Leaking credentials or internal IPs	Return only status, duration, generic details
Missing checks	Silent dependency failures	Register checkers for all critical dependencies
Synchronous only	Sequential checks increase latency	Consider parallel execution for many checks
No degraded state	Binary healthy/unhealthy is too rigid	Use three-state model with Degraded

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References

For complete PHP templates and examples, see:

• references/templates.md — HealthCheckInterface, HealthStatus, HealthCheckResult, checkers, runner, action templates
• references/examples.md — DI wiring, custom checker, and unit tests