fix: enhance health check functionality with detailed memory diagnostics and stable liveness probe

app/api/health/route.ts

@@ -1,10 +1,21 @@
+import v8 from 'node:v8';
 import { NextResponse } from 'next/server';
 import { NextRequest } from 'next/server';
 import { logger } from '@/lib/logger';
 
-// Health check thresholds
-const MEMORY_WARNING_THRESHOLD = 0.85; // 85% heap usage
-const MEMORY_CRITICAL_THRESHOLD = 0.95; // 95% heap usage
+const MEMORY_WARNING_THRESHOLD = 0.85;
+const MEMORY_CRITICAL_THRESHOLD = 0.95;
+
+function getHeapUsagePercent(heapUsed: number, heapTotal: number): number {
+  const heapSizeLimit = v8.getHeapStatistics().heap_size_limit;
+  const denominator = heapSizeLimit > 0 ? heapSizeLimit : heapTotal;
+
+  if (denominator <= 0) {
+    return 0;
+  }
+
+  return (heapUsed / denominator) * 100;
+}
 
 interface HealthStatus {
   status: 'healthy' | 'degraded' | 'unhealthy';
@@ -14,6 +25,7 @@ interface HealthStatus {
   memory?: {
     heapUsed: number;
     heapTotal: number;
+    heapSizeLimit: number;
     rss: number;
     external: number;
     heapUsagePercent: number;
@@ -27,14 +39,9 @@ interface HealthStatus {
 /**
  * Health check endpoint for container orchestration
  *
- * GET /api/health - Basic health check (returns 200 OK or 503 Service Unavailable)
- * GET /api/health?detailed=true - Detailed diagnostics with memory stats
- * HEAD /api/health - Lightweight health check (status code only)
- *
- * Health status based on Node.js heap usage:
- * - Healthy (200): < 85% heap usage
- * - Degraded (200): 85-95% heap usage (warnings in detailed mode)
- * - Unhealthy (503): > 95% heap usage
+ * GET /api/health - Liveness probe for container orchestration
+ * GET /api/health?detailed=true - Diagnostics with advisory memory warnings
+ * HEAD /api/health - Lightweight liveness probe (status code only)
  */
 export async function GET(request: NextRequest) {
   const searchParams = request.nextUrl.searchParams;
@@ -43,38 +50,31 @@ export async function GET(request: NextRequest) {
   try {
     const timestamp = new Date().toISOString();
     const memUsage = process.memoryUsage();
-    const heapUsagePercent = (memUsage.heapUsed / memUsage.heapTotal) * 100;
-
-    // Determine health status based on memory usage
+    const heapSizeLimit = v8.getHeapStatistics().heap_size_limit;
+    const heapUsagePercent = getHeapUsagePercent(memUsage.heapUsed, memUsage.heapTotal);
     let status: 'healthy' | 'degraded' | 'unhealthy' = 'healthy';
     const warnings: string[] = [];
-    let httpStatus = 200;
 
     if (heapUsagePercent >= MEMORY_CRITICAL_THRESHOLD * 100) {
-      status = 'unhealthy';
-      httpStatus = 503;
+      status = 'degraded';
+      warnings.push(`V8 heap usage is very high: ${heapUsagePercent.toFixed(1)}% of heap limit`);
     } else if (heapUsagePercent >= MEMORY_WARNING_THRESHOLD * 100) {
       status = 'degraded';
-      warnings.push(`Memory usage high: ${heapUsagePercent.toFixed(1)}%`);
+      warnings.push(`V8 heap usage is high: ${heapUsagePercent.toFixed(1)}% of heap limit`);
     }
 
-    // Build response
     const response: HealthStatus = {
-      status,
+      status: detailed ? status : 'healthy',
       timestamp,
     };
 
-    if (status === 'unhealthy') {
-      response.reason = `Memory usage critical: ${heapUsagePercent.toFixed(1)}%`;
-    }
-
-    // Add detailed information if requested
     if (detailed) {
       response.uptime = process.uptime();
       response.version = process.env.npm_package_version || '0.1.0';
       response.memory = {
         heapUsed: memUsage.heapUsed,
         heapTotal: memUsage.heapTotal,
+        heapSizeLimit,
         rss: memUsage.rss,
         external: memUsage.external,
         heapUsagePercent: Number(heapUsagePercent.toFixed(2)),
@@ -87,10 +87,8 @@ export async function GET(request: NextRequest) {
       }
     }
 
-    logger.info('Health check', { status, detailed });
-
     return NextResponse.json(response, {
-      status: httpStatus,
+      status: 200,
       headers: {
         'Cache-Control': 'no-store, no-cache, must-revalidate',
         'Pragma': 'no-cache',
@@ -116,13 +114,6 @@ export async function GET(request: NextRequest) {
  */
 export async function HEAD() {
   try {
-    const memUsage = process.memoryUsage();
-    const heapUsagePercent = (memUsage.heapUsed / memUsage.heapTotal) * 100;
-
-    if (heapUsagePercent >= MEMORY_CRITICAL_THRESHOLD * 100) {
-      return new Response(null, { status: 503 });
-    }
-
     return new Response(null, { status: 200 });
   } catch {
     return new Response(null, { status: 503 });

lib/__tests__/health-route.test.ts

@@ -0,0 +1,98 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+
+const loggerError = vi.fn();
+
+vi.mock('next/server', () => ({
+  NextResponse: {
+    json: (data: unknown, init?: { status?: number; headers?: unknown }) => ({
+      status: init?.status ?? 200,
+      headers: init?.headers,
+      json: async () => data,
+    }),
+  },
+}));
+
+vi.mock('@/lib/logger', () => ({
+  logger: {
+    error: loggerError,
+  },
+}));
+
+describe('health route', () => {
+  beforeEach(() => {
+    vi.restoreAllMocks();
+    loggerError.mockReset();
+  });
+
+  it('returns healthy for the basic liveness probe even when heap usage is high', async () => {
+    vi.spyOn(process, 'memoryUsage').mockReturnValue({
+      rss: 120_000_000,
+      heapTotal: 45_000_000,
+      heapUsed: 43_000_000,
+      external: 8_000_000,
+      arrayBuffers: 1_000_000,
+    });
+
+    const { GET } = await import('@/app/api/health/route');
+    const response = await GET({ nextUrl: new URL('http://localhost/api/health') } as never);
+    const payload = await response.json();
+
+    expect(response.status).toBe(200);
+    expect(payload).toMatchObject({
+      status: 'healthy',
+    });
+    expect(payload.warnings).toBeUndefined();
+  });
+
+  it('returns degraded diagnostics in detailed mode without failing the probe', async () => {
+    vi.spyOn(process, 'memoryUsage').mockReturnValue({
+      rss: 120_000_000,
+      heapTotal: 4_100_000_000,
+      heapUsed: 4_000_000_000,
+      external: 8_000_000,
+      arrayBuffers: 1_000_000,
+    });
+    vi.spyOn(process, 'uptime').mockReturnValue(123.45);
+
+    const { GET } = await import('@/app/api/health/route');
+    const response = await GET({ nextUrl: new URL('http://localhost/api/health?detailed=true') } as never);
+    const payload = await response.json();
+
+    expect(response.status).toBe(200);
+    expect(payload.status).toBe('degraded');
+    expect(payload.memory).toMatchObject({
+      heapUsed: 4_000_000_000,
+      heapTotal: 4_100_000_000,
+      rss: 120_000_000,
+      external: 8_000_000,
+    });
+    expect(payload.memory.heapSizeLimit).toBeGreaterThan(0);
+    expect(payload.warnings).toEqual([
+      expect.stringContaining('V8 heap usage is high'),
+    ]);
+  });
+
+  it('keeps HEAD as a stable liveness probe', async () => {
+    const { HEAD } = await import('@/app/api/health/route');
+    const response = await HEAD();
+
+    expect(response.status).toBe(200);
+  });
+
+  it('returns 503 when collecting health diagnostics throws', async () => {
+    vi.spyOn(process, 'memoryUsage').mockImplementation(() => {
+      throw new Error('boom');
+    });
+
+    const { GET } = await import('@/app/api/health/route');
+    const response = await GET({ nextUrl: new URL('http://localhost/api/health') } as never);
+    const payload = await response.json();
+
+    expect(response.status).toBe(503);
+    expect(payload).toMatchObject({
+      status: 'unhealthy',
+      reason: 'boom',
+    });
+    expect(loggerError).toHaveBeenCalledWith('Health check failed', { error: 'boom' });
+  });
+});