feat(monitoring): add /api/metrics endpoint for Prometheus scraping

memento-note/app/api/metrics/route.ts

@@ -0,0 +1,68 @@
+import { NextResponse } from 'next/server'
+import { prisma } from '@/lib/prisma'
+import { redis } from '@/lib/redis'
+
+export const dynamic = 'force-dynamic'
+
+export async function GET() {
+  const lines: string[] = []
+
+  const metric = (name: string, help: string, type: string, value: number | string, labels = '') => {
+    lines.push(`# HELP ${name} ${help}`)
+    lines.push(`# TYPE ${name} ${type}`)
+    lines.push(labels ? `${name}{${labels}} ${value}` : `${name} ${value}`)
+  }
+
+  // Uptime
+  metric('memento_uptime_seconds', 'Application uptime in seconds', 'gauge', process.uptime().toFixed(2))
+
+  // Database
+  try {
+    const dbStart = Date.now()
+    const [noteCount, notebookCount, userCount] = await Promise.all([
+      prisma.note.count(),
+      prisma.notebook.count(),
+      prisma.user.count(),
+    ])
+    const dbLatency = Date.now() - dbStart
+    metric('memento_db_up', 'Database connectivity (1=up, 0=down)', 'gauge', 1)
+    metric('memento_db_latency_ms', 'Database query latency in milliseconds', 'gauge', dbLatency)
+    metric('memento_notes_total', 'Total number of notes', 'gauge', noteCount)
+    metric('memento_notebooks_total', 'Total number of notebooks', 'gauge', notebookCount)
+    metric('memento_users_total', 'Total number of users', 'gauge', userCount)
+  } catch {
+    metric('memento_db_up', 'Database connectivity (1=up, 0=down)', 'gauge', 0)
+  }
+
+  // Redis
+  try {
+    const redisStart = Date.now()
+    await redis.ping()
+    const dbSize = await redis.dbsize()
+    const info = await redis.info('memory')
+    const redisLatency = Date.now() - redisStart
+    const memMatch = info.match(/used_memory:(\d+)/)
+    const usedMemoryBytes = memMatch ? parseInt(memMatch[1]) : 0
+    metric('memento_redis_up', 'Redis connectivity (1=up, 0=down)', 'gauge', 1)
+    metric('memento_redis_latency_ms', 'Redis ping latency in milliseconds', 'gauge', redisLatency)
+    metric('memento_redis_keys_total', 'Total number of Redis keys', 'gauge', dbSize)
+    metric('memento_redis_memory_bytes', 'Redis used memory in bytes', 'gauge', usedMemoryBytes)
+  } catch {
+    metric('memento_redis_up', 'Redis connectivity (1=up, 0=down)', 'gauge', 0)
+  }
+
+  // Node.js process memory
+  const mem = process.memoryUsage()
+  metric('memento_process_heap_used_bytes', 'Node.js heap used in bytes', 'gauge', mem.heapUsed)
+  metric('memento_process_heap_total_bytes', 'Node.js heap total in bytes', 'gauge', mem.heapTotal)
+  metric('memento_process_rss_bytes', 'Node.js RSS memory in bytes', 'gauge', mem.rss)
+
+  const body = lines.join('\n') + '\n'
+
+  return new NextResponse(body, {
+    status: 200,
+    headers: {
+      'Content-Type': 'text/plain; version=0.0.4; charset=utf-8',
+    },
+  })
+}