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 });