---
title: Monitoring
tags: [operations]
---

# Monitoring

What's instrumented today and what to watch. Today's stack is intentionally lean — health endpoints, Docker healthchecks, Sentry, and access logs. Bigger metric pipelines (Prometheus, Grafana, OpenSearch) are a future addition.

---

## 1. Health endpoint

Path: `GET /health` (backend, port `5001`).

Defined in `backend/src/app.ts`:

```ts
app.get("/health", (req, res) => {
  res.json({
    success: true,
    message: "Marketplace Backend API is running",
    timestamp: new Date().toISOString(),
    environment: config.nodeEnv,
    version: packageJson.version,
  });
});
```

Returns `200` with a JSON envelope as soon as Express is up. Does **not** currently probe MongoDB or Redis — they are checked via separate Docker healthchecks. If you want deep health, extend the endpoint to ping both data stores and return `503` on failure.

Public URL behind Nginx: `https://amn.gg/api/health`.

---

## 2. Docker healthchecks

Each long-lived container has a `HEALTHCHECK` baked in or declared in compose.

| Container | Probe | Interval | Failure threshold |
|-----------|-------|----------|-------------------|
| `nickapp-backend` | `node healthcheck.js` (HTTP GET `/health`) | 30s | 3 retries |
| `nickapp-frontend` | `curl -f http://localhost:8083/` | 30s | 3 retries |
| `mongodb` | `mongosh --eval "db.adminCommand('ping')"` | 30s | 3 retries |
| `redis` | `redis-cli -a $REDIS_PASSWORD ping` | 30s | 3 retries |

`healthcheck.js` (backend) is a tiny Node script that does a local HTTP GET to `/health` and exits 0 / 1.

Inspect health:

```bash
docker ps --format "table {{.Names}}\t{{.Status}}"

# Detailed
docker inspect --format='{{json .State.Health}}' nickapp-backend | jq
```

If a container is `unhealthy`, Watchtower will **not** roll it (it expects the new container to pass healthcheck). Investigate with `docker logs <container>`.

---

## 3. Sentry — error tracking

### Frontend

`@sentry/nextjs ^10.22.0` is wired in via three config files at the repo root:

- `sentry.client.config.ts` — browser SDK (with Session Replay enabled at 10% session / 100% error rate).
- `sentry.server.config.ts` — server-rendered components (no Replay).
- `sentry.edge.config.ts` — edge runtime (not currently used heavily).

Common settings:

```ts
Sentry.init({
  dsn: process.env.NEXT_PUBLIC_SENTRY_DSN,
  tracesSampleRate: process.env.NODE_ENV === 'production' ? 0.1 : 1.0,
  environment: process.env.NODE_ENV || 'development',
  enabled: process.env.NODE_ENV === 'production',
  ignoreErrors: ['ResizeObserver loop limit exceeded', 'ChunkLoadError', ...],
});
```

Errors from `localhost` are filtered out — only prod errors land in the dashboard.

### Backend

`@sentry/node ^10.22.0` + `@sentry/profiling-node ^10.22.0` are initialised **first** in `src/app.ts` (before any other import) via `src/config/sentry.ts`. DSN comes from `SENTRY_DSN` env var (see [[Environment Variables#sentry]]).

What's captured:

- Uncaught exceptions in route handlers
- Promise rejections inside `asyncHandler`-wrapped routes
- Manually-captured errors via `Sentry.captureException(err)`
- Performance traces (10% sample rate in prod)
- Profiling samples via `@sentry/profiling-node`

### Source maps

Frontend uploads source maps to Sentry at build time when `SENTRY_AUTH_TOKEN`, `SENTRY_ORG`, and `SENTRY_PROJECT` are set in the CI env. Without them the build still succeeds but Sentry traces will show minified frames.

### Alerts

Configure in the Sentry dashboard (Issues → Alerts) — common alerts:

- Any new issue in production → Slack
- Error frequency > 50/minute → page on-call
- Performance regression on `/api/payments/*` traces → email

---

## 4. Logs

### Backend application logs

Routed through `src/utils/logger.ts` — currently a thin `console.log` wrapper with emoji prefixes. Output goes to stdout, captured by Docker:

```bash
# Live tail
docker compose -f docker-compose.production.yml logs -f --tail=200 nickapp-backend

# Search for a request
docker logs nickapp-backend 2>&1 | grep "POST /api/payments"

# Pre-filter by date
docker logs --since 1h nickapp-backend
```

Notable log lines to look for:

| Prefix | Meaning |
|--------|---------|
| `✅ Connected to MongoDB` | DB connection established |
| `🚀 Server running on port 5001` | App fully started |
| `🔌 User connected: <id>` | Socket.IO connection |
| `📥` | Inbound HTTP request log |
| `💳 SHKeeper` | SHKeeper webhook / API call |
| `🔐 Webhook verification` | Webhook signature check result |
| `❌ Error` | Manual error log (also captured by Sentry) |

### Nginx access + error logs

Bind-mounted to `./nginx/logs/` on the host:

```bash
tail -f /opt/backend/nginx/logs/access.log
tail -f /opt/backend/nginx/logs/error.log
```

Rotate these via host `logrotate` to avoid disk fill.

### Frontend logs

Next.js logs go to the container stdout:

```bash
docker logs -f nickapp-frontend
```

Browser-side logs that need attention go through Sentry (above) — `src/utils/logger.ts` in the frontend forwards via Sentry breadcrumbs.

---

## 5. Key metrics to watch

Today these are read manually from logs / Sentry. As Prometheus is added, encode them as alerting rules.

### Application

| Metric | Where to check | Healthy | Alert |
|--------|---------------|---------|-------|
| 5xx rate | Sentry, Nginx access.log | < 0.5 % | > 2 % over 5 min |
| `/health` p95 latency | curl + timer | < 100 ms | > 1 s |
| Login success rate | Sentry custom event | > 95 % | < 90 % |
| Socket disconnect storm | `🔌 User disconnected` log frequency | < 1/s sustained | > 10/s sustained |
| OpenAI 429s | Backend log `OpenAI ... 429` | 0 | any |

### Payments

| Metric | Where | Healthy | Alert |
|--------|-------|---------|-------|
| Payment success rate | `db.payments.aggregate([{$group:{_id:"$status",n:{$sum:1}}}])` | > 95 % completed of 24h-old payments | < 90 % |
| Webhook signature failures | log `Webhook verification failed` | 0 | > 0 |
| Request Network webhook 4xx | nginx access log `/api/payment/request-network/webhook` | 0 | any real provider delivery returning 4xx |
| Request Network safety-pending payments | `db.payments.find({"metadata.transactionSafety.status":"pending"})` | explained/short-lived | pending > 10 min without operator note |
| SHKeeper API errors (5xx) | log + Sentry | 0 | > 5/min sustained |
| Payouts stuck in `pending` > 30 min | `db.payments.find({type:'payout',status:'pending',createdAt:{$lt:ISODate(30 min ago)}})` | empty | non-empty |
| Missing `transactionHash` after `completed` | the same query that drives `fix-transaction-hashes.js` | empty | non-empty |

### MongoDB

```js
db.serverStatus().connections           // active connections; alert if >1000
db.serverStatus().opcounters            // ops/sec
db.serverStatus().wiredTiger.cache      // cache hit ratio; aim > 95 %
db.currentOp({ secs_running: { $gte: 5 } })  // long-running queries
```

### Redis

```bash
docker exec nickapp-redis redis-cli -a "$REDIS_PASSWORD" INFO stats
# Watch: instantaneous_ops_per_sec, keyspace_hits/misses, rejected_connections, evicted_keys
```

Alert thresholds: `rejected_connections > 0`, `evicted_keys` rising while you don't expect cache pressure, `latency_ms` p99 > 5ms.

### Host

| Metric | Tool | Healthy | Alert |
|--------|------|---------|-------|
| Disk usage on `/var/lib/docker` | `df -h` | < 80 % | > 90 % |
| `/opt/backend/uploads` size | `du -sh` | watch trend | bursty growth (>5 GB/day) |
| Memory pressure | `free -h`, `docker stats` | < 80 % | swap actively used |
| Open file descriptors | `cat /proc/<pid>/limits` | well under hard limit | nearing limit |

---

## 6. Smoke tests after a deploy

Drop these in a runbook for the on-call:

```bash
# 1. API health
curl -fsS https://amn.gg/api/health | jq '.success,.version,.environment'

# 2. Login
curl -fsS -X POST https://amn.gg/api/auth/login \
  -H "Content-Type: application/json" \
  -d '{"email":"admin@marketplace.com","password":"<prod-admin-pwd>"}' \
  | jq '.success,.data.user.email'

# 3. Frontend HTML loads
curl -fsS https://amn.gg/ -I | head -1   # expect 200

# 4. Socket.IO handshake
curl -fsS "https://amn.gg/socket.io/?EIO=4&transport=polling" -I | head -1

# 5. Containers healthy
docker ps --filter "name=nickapp-" --format "table {{.Names}}\t{{.Status}}"
```

Any non-OK → see [[Incident Response]].

---

## 7. Future work

- **Prometheus + Grafana** with Node exporter + Mongo exporter + Redis exporter — for proper time-series.
- **OpenTelemetry** spans from backend → Sentry / Jaeger.
- **Healthcheck endpoint** that probes Mongo + Redis and returns `503` when degraded.
- **PagerDuty / OpsGenie** wiring from Sentry alerts.
- **Synthetic checks** (Pingdom / UptimeRobot) hitting `/health` from multiple regions.

For now, Sentry + Docker healthchecks + manual log checks cover the basics. See [[Incident Response]] for what to do when something fires.