Finchippay-Solution/PR_METRICS.md at master · Emmanueljr-stack/Finchippay-Solution

Summary

This PR implements a Prometheus-compatible observability stack for the Finchippay backend, addressing the complete absence of production metrics (Issue #79). It adds a GET /metrics endpoint exposing request rates, P95 latency, Horizon API call volumes, active webhook SSE streams, and default Node.js runtime metrics — all in Prometheus text format. The endpoint is protected by Bearer token authentication via a METRICS_TOKEN environment variable. A pre-built Grafana dashboard and a ready-to-run Prometheus + Grafana Docker Compose stack ship alongside the implementation so operators can visualize data within minutes of merging.

Closes #79

Type of change

New feature (Prometheus metrics exposition + observability stack)
Tests (5 new unit tests for METRICS_TOKEN validation)
Documentation (ENV.md, inline JSDoc, dashboard JSON, Prometheus config)
Configuration change (docker-compose.yml, docker-compose.prod.yml)

Architecture

┌──────────────┐     scrape /metrics      ┌─────────────┐     query     ┌──────────┐
│  Prometheus  │ ◄─────────────────────► │   Backend   │              │ Grafana  │
│  :9090       │     Bearer <token>       │   Express   │              │ :3001    │
└──────────────┘                          │   :4000     │              └──────────┘
                                          └─────────────┘
                                                 │
                                   ┌─────────────┼─────────────┐
                                   │             │             │
                              trackHttpMetrics  stellarService  webhookService
                              (every request)   (horizon calls)  (SSE streams)

Data flow

trackHttpMetrics middleware (mounted immediately after helmet, before routes) attaches a finish event listener on every request. When the response completes, it records:
- Duration via http_request_duration_seconds histogram (high-resolution process.hrtime.bigint())
- Count via http_requests_total counter labeled by method, normalised route, and status code
stellarService.js increments horizon_requests_total on every Horizon API call (loadAccount, getPayments, getTransaction) tagged success or error.
webhookService.js increments horizon_requests_total on SSE stream starts and errors, and updates active_webhook_streams gauge whenever a stream is created or torn down.
GET /metrics renders the prom-client registry as Prometheus text format. Protected by requireMetricsToken middleware (Bearer auth via METRICS_TOKEN).

Files Changed

New files (6)

File	Lines	Purpose
`backend/src/services/metricsService.js`	101	Creates a dedicated `prom-client` Registry with `finchippay_` prefix. Registers 4 custom metrics + `collectDefaultMetrics()` for Node.js runtime instrumentation. Exports `getMetrics()` and `getContentType()` for use by the route handler.
`backend/src/middleware/metrics.js`	108	Exports `trackHttpMetrics` (duration + counter middleware) and `requireMetricsToken` (Bearer auth gate for `/metrics`). Includes `normalisedRoute()` to collapse dynamic Express paths like `/api/payments/:id` to stable label values.
`backend/src/routes/metrics.js`	40	Express router exposing `GET /metrics`. Calls `requireMetricsToken` before the handler. Renders the Prometheus text payload with correct `Content-Type`.
`docs/prometheus.yml`	31	Prometheus scrape config targeting `backend:4000/metrics` every 15 s. Includes commented instructions for adding Bearer auth in production.
`docs/grafana-dashboard.json`	500+	8-panel Grafana dashboard (schema v39) covering HTTP rate, P50/P95 latency, success rate, 5xx rate, webhook streams, heap memory, Horizon rate, and CPU usage.
`docs/grafana-datasources.yml`	17	Grafana provisioning config that auto-wires the Prometheus datasource with uid `prometheus`.

Modified files (11)

File	Change summary
`backend/package.json`	Added `prom-client` dependency
`backend/package-lock.json`	Lockfile updated (651 new packages)
`backend/src/server.js`	Imported `trackHttpMetrics` and `metricsRoutes`; mounted middleware after helmet + before `pinoHttp`; registered `/metrics` route after all API routes
`backend/src/services/stellarService.js`	Imported `metricsService`; added `horizonRequestsTotal.inc()` at 5 instrumentation points: `loadAccount` success/error, `getPayments` success/error (via try/catch), `getTransaction` success/error
`backend/src/services/webhookService.js`	Imported `metricsService`; added `horizonRequestsTotal.inc({ operation: "startSSE" })` before the stream-exists check; added `horizonRequestsTotal.inc({ operation: "sse", status: "error" })` in the `onerror` callback; set `activeWebhookStreams` gauge on stream creation and teardown
`backend/src/config/validateEnv.js`	Added `METRICS_TOKEN` validation: optional but if set must be ≥ 16 characters; generates actionable error message
`backend/__tests__/validateEnv.test.js`	5 new test cases: absent token → no error; valid ≥16 chars → no error; too-short → flagged; exactly 16 chars → no error; whitespace-only → treated as absent
`docker-compose.yml`	Added `prometheus` (port 9090, `--web.enable-lifecycle`) and `grafana` (port 3001, admin/admin) services with named volumes `prometheus_data` and `grafana_data`
`docker-compose.prod.yml`	Same as above but Prometheus + Grafana bind to `127.0.0.1` only; Prometheus uses 30-day retention; Grafana credentials via `${GRAFANA_ADMIN_USER}` / `${GRAFANA_ADMIN_PASSWORD}` env vars
`ENV.md`	Added `METRICS_TOKEN` row to the backend env vars table (optional, ≥ 16 chars, `openssl rand -hex 32`)
`package-lock.json` (root)	Updated

Custom Metrics — Detailed Specification

1. `http_requests_total` (Counter)

labels: method, route, status_code

Incremented on every completed HTTP request. The route label uses the normalised Express pattern (e.g. GET /api/payments/:id) rather than the raw URL path, preventing unbounded cardinality from dynamic segments like account IDs or payment hashes.

Normalisation logic (normalisedRoute in middleware/metrics.js):

Reads req.route.path (resolved after Express matches the route) plus req.baseUrl for mounted sub-routers
Falls back to req.path for unmatched routes (e.g. 404s)
Produces labels like GET /health, POST /api/payments/:id, GET /federation

2. `http_request_duration_seconds` (Histogram)

labels: method, route
buckets: [0.05, 0.1, 0.5, 1, 2, 5]

Measured from middleware entry to the finish event on res, using process.hrtime.bigint() for nanosecond precision. The histogram buckets are tuned for API response times:

50 ms: sub-100 ms fast-path responses (cached account lookups, health checks)
100 ms: typical JSON API response
500 ms: slower queries (Horizon payment history without cache)
1–2 s: long-tail external API calls
5 s: timeout boundary

Query for P95 in PromQL: histogram_quantile(0.95, rate(http_request_duration_seconds_bucket[2m]))

3. `horizon_requests_total` (Counter)

labels: operation, status

Tracks all outbound calls to the Stellar Horizon API. Instrumentation points:

Operation	Location	Success condition	Error condition
`loadAccount`	`stellarService.getAccount()`	Horizon returns account data	404 or network error after retries
`getPayments`	`stellarService.getPayments()`	`query.call()` succeeds	Exception from `withTimeoutAndRetry`
`getTransaction`	`stellarService.getPayments()` (per-payment memo fetch)	Transaction object returned	Exception caught, memo skipped
`startSSE`	`webhookService.startMonitoring()`	Called (always succeeds synchronously)	N/A
`sse`	`webhookService.startMonitoring()` `onerror` callback	N/A	SSE stream error

4. `active_webhook_streams` (Gauge)

labels: (none)

Reflects activeStreams.size — the number of concurrently open Horizon SSE connections. Updated:

Incremented: after activeStreams.set() in startMonitoring()
Decremented: after activeStreams.delete() in the onerror callback

Default Node.js metrics (`collectDefaultMetrics`)

Registered with prefix: "finchippay_" via prom-client's built-in collector. Exposes:

Metric	Description
`finchippay_process_cpu_user_seconds_total`	User CPU time
`finchippay_process_cpu_system_seconds_total`	System CPU time
`finchippay_process_heap_bytes`	V8 heap size
`finchippay_process_resident_memory_bytes`	RSS
`finchippay_nodejs_eventloop_lag_seconds`	Event loop lag (P50/P95/P99)
`finchippay_nodejs_gc_duration_seconds`	GC pause duration
... and more	file descriptors, active handles, heap spaces

Authentication Design

Token-based Bearer auth (`requireMetricsToken` middleware)

Authorization: Bearer <METRICS_TOKEN>

Three modes of operation:

Mode	`METRICS_TOKEN` set?	Behavior
Local dev	No	`/metrics` is open; a `console.warn` is emitted once at startup reminding the developer to set it in production
Test	No (`NODE_ENV=test`)	Open, but the warning is suppressed to keep test output clean
Production	Yes (≥ 16 chars)	`401 Unauthorized` returned unless the `Authorization: Bearer <token>` header matches exactly

Error responses:

Missing/invalid header → 401 + WWW-Authenticate: Bearer realm="metrics" + JSON {"error": "Unauthorized: missing or invalid Authorization header..."}
Wrong token → 401 + JSON {"error": "Unauthorized: invalid metrics token."}

Startup validation (`validateEnv.js`)

METRICS_TOKEN is optional (no startup crash if missing). When present:

Must be a string of ≥ 16 characters (non-whitespace)
Shorter tokens cause process.exit(1) with: METRICS_TOKEN must be at least 16 characters, got N. Generate a secure token: openssl rand -hex 32
Whitespace-only is treated as absent (development fallback)

Prometheus scraper auth

The docs/prometheus.yml config file ships without the authorization block (open access for local dev). Comments in the file instruct operators to uncomment and configure the block for production:

# authorization:
#   type: "Bearer"
#   credentials: "YOUR_METRICS_TOKEN"

Note: Prometheus does not perform env-var substitution in config files — the token must be inlined or injected via a pre-processing step (e.g. envsubst in a custom entrypoint). The comments make this explicit.

Grafana Dashboard

Title: Finchippay Solution — Backend Metrics UID: finchippay-backend-metrics Refresh: 30 s Default range: Last 1 hour

Panel layout (24-column grid, 8 panels)

Row	Panel	Type	Size	PromQL
1	HTTP Request Rate	Timeseries (line)	12×8	`rate(http_requests_total[1m])`
1	HTTP Request Duration (P50 & P95)	Timeseries (line)	12×8	`histogram_quantile(0.95, rate(http_request_duration_seconds_bucket[2m]))` + P50 variant
2	Success Rate (2xx)	Stat (background)	6×6	`sum(rate(http_requests_total{status_code=~"2.."}[5m])) / sum(rate(http_requests_total[5m])) * 100`
2	5xx Error Rate	Stat (background)	6×6	`sum(rate(http_requests_total{status_code=~"5.."}[5m]))`
2	Active Webhook Streams	Stat (background)	6×6	`active_webhook_streams`
2	Heap Memory	Stat (background)	6×6	`finchippay_process_heap_bytes`
3	Horizon Request Rate	Timeseries (line)	12×8	`rate(horizon_requests_total[1m])`
3	CPU Usage	Timeseries (line)	12×8	`rate(finchippay_process_cpu_user_seconds_total[1m]) * 100` + system variant

All stat panels use background color mode with area sparklines for at-a-glance health assessment. Timeseries panels use smooth line interpolation with table legends showing mean and max.

The dashboard is provisioned into Grafana automatically via volume mount (/etc/grafana/provisioning/dashboards/finchippay.json), so it appears immediately after docker compose up — no manual import needed.

Design Decisions

1. Why `process.hrtime.bigint()` instead of `Date.now()`?

Date.now() has millisecond resolution and is subject to system clock adjustments (NTP skew, manual changes). process.hrtime.bigint() provides nanosecond-precision monotonic time — essential for accurate latency histograms where 50 ms buckets need meaningful data. The conversion Number(bigint) / 1e9 avoids floating-point drift.

2. Why route normalisation via `req.route.path`?

Without normalisation, a Prometheus scrape would produce separate time-series for every unique URL path (e.g. /api/payments/GABC...123, /api/payments/GXYZ...789), quickly reaching hundreds of thousands of series and overwhelming Prometheus storage. Express stores the matched route pattern on req.route.path after resolution — using this yields stable labels like GET /api/payments/:id.

3. Why a dedicated `prom-client` Registry instead of the default global?

A dedicated Registry instance (not promClient.register) isolates Finchippay metrics from any other libraries that might register metrics on the global default. The prefix: "finchippay_" applied to collectDefaultMetrics further prevents naming collisions with other services on the same Prometheus instance.

4. Why mount `trackHttpMetrics` before `pinoHttp`?

Ordering matters for accurate latency measurement:

helmet — sets security headers (no measurable impact)
trackHttpMetrics — starts the high-resolution timer immediately
pinoHttp — request logging (excluded from timing)
express.json — body parsing (included in timing, as it's part of request processing)
Routes — business logic (included in timing)

This ensures the duration captures actual request processing time, not just route handler execution.

5. Why the `/metrics` route is subject to the global rate limiter?

The global limiter (100 req / 15 min per IP) is adequate for typical Prometheus scrape intervals (15–60 s ≈ 15–60 req / 15 min). Moving the route above the limiter would require refactoring the middleware pipeline and is unnecessary for standard configurations. A comment in routes/metrics.js documents this trade-off for operators who scrape more aggressively.

6. Why no test for the `/metrics` endpoint itself?

The existing backend test suite uses unit + property-based tests (Jest, fast-check) rather than HTTP-level integration tests (supertest). The validateEnv.test.js tests cover the METRICS_TOKEN validation logic. An HTTP-level integration test for the /metrics endpoint would be a valuable follow-up but is consistent with the current testing strategy to defer.

Testing

New tests added

Test	File	What it verifies
METRICS_TOKEN absent → no error	`validateEnv.test.js`	Optional env var doesn't block startup
METRICS_TOKEN ≥ 16 chars → no error	`validateEnv.test.js`	Valid tokens pass validation
METRICS_TOKEN too short → error	`validateEnv.test.js`	Short tokens are flagged with actionable message
METRICS_TOKEN exactly 16 chars → no error	`validateEnv.test.js`	Boundary case: minimum length accepted
METRICS_TOKEN whitespace-only → no error	`validateEnv.test.js`	Empty/whitespace treated as absent (dev fallback)

Existing tests (regression)

All 107 existing backend tests continue to pass without modification. The metrics instrumentation is purely additive — it adds counter/gauge increments after existing logic without altering any return values, error handling, or control flow.

How to Test

Local development (Docker Compose)

# 1. Start the full stack (backend, frontend, Prometheus, Grafana)
docker compose up

# 2. Verify the /metrics endpoint is live (open in dev)
curl -s http://localhost:4000/metrics | head -20
# Expected output:
# # HELP finchippay_process_cpu_user_seconds_total ...
# # TYPE finchippay_process_cpu_user_seconds_total counter
# # HELP http_requests_total Total number of HTTP requests...
# # TYPE http_requests_total counter
# ...

# 3. Generate some traffic to populate metrics
curl http://localhost:4000/health
curl http://localhost:4000/api/auth/nonce  # or any valid endpoint

# 4. Open Grafana at http://localhost:3001
#    Credentials: admin / admin
#    Dashboard: "Finchippay Solution — Backend Metrics"
#    You should see the HTTP Request Rate panel showing recent requests.

# 5. Verify Prometheus is scraping successfully
#    Open http://localhost:9090/targets
#    The "finchippay-backend" target should show State: UP

With METRICS_TOKEN (simulates production)

# Start backend with a token
cd backend
METRICS_TOKEN=my-production-token-32chars npm start

# Without token → 401
curl -i http://localhost:4000/metrics
# HTTP/1.1 401 Unauthorized
# www-authenticate: Bearer realm="metrics"
# {"error":"Unauthorized: missing or invalid Authorization header..."}

# With correct token → 200
curl -H "Authorization: Bearer my-production-token-32chars" http://localhost:4000/metrics

# With wrong token → 401
curl -H "Authorization: Bearer wrong-token" http://localhost:4000/metrics
# {"error":"Unauthorized: invalid metrics token."}

Verify individual metrics

# HTTP request counter — look for health check requests
curl -s http://localhost:4000/metrics | grep 'http_requests_total{'

# Horizon request counter — make some Stellar calls first
curl -s http://localhost:4000/metrics | grep 'horizon_requests_total{'

# Active webhook streams — should be 0 initially
curl -s http://localhost:4000/metrics | grep 'active_webhook_streams'

# Default Node.js metrics — prefixed with finchippay_
curl -s http://localhost:4000/metrics | grep 'finchippay_process_heap_bytes'

CI Verification

All CI jobs that are affected by this change pass locally:

Check	Status	Details
Backend lint (`eslint`)	✅ 0 errors	All new `.js` files follow `eslint:recommended` + `prettier`
Backend tests (`jest`)	✅ 12/12 suites, 107/107 tests	Including 5 new `validateEnv` tests
Docker Compose config validation	✅ Both valid	`docker-compose.yml` and `docker-compose.prod.yml`

Jobs unaffected (no changes in these domains):

Job	Reason untouched
Frontend (lint, type-check, tests, build)	No frontend files modified
Contracts (cargo check, cargo test, WASM build)	No Rust files modified
E2E (Playwright)	No UI changes; backend API surface extended but not altered

Backward Compatibility

✅ No breaking changes. All existing routes, middleware, error handling, and response formats are preserved.
✅ Optional env var. METRICS_TOKEN is not required; the server starts and operates normally without it.
✅ Additive instrumentation. Counter and gauge increments are side-effect-free — they do not alter return values, throw exceptions, or change control flow.
✅ No new required dependencies for existing services. prom-client is only needed in the backend; frontend and contracts are unaffected.
✅ Docker Compose additive. The prometheus and grafana services are added alongside existing services; docker compose up backend frontend still works to run only the core stack.

Security Considerations

Metrics do not expose sensitive data. The /metrics endpoint returns aggregate counters and histograms — no Stellar public keys, transaction hashes, user data, or request payloads are exposed.
Token-based access control. When METRICS_TOKEN is set in production, only Prometheus (or an authorized scraper) can access the endpoint. The token is compared with a constant-time-safe string comparison.
No token in logs. The METRICS_TOKEN value never appears in logs, error messages, or response bodies.
Prometheus + Grafana bind to localhost in production. The docker-compose.prod.yml uses 127.0.0.1 port bindings so the monitoring stack is not exposed to the public internet.

Acceptance Criteria Checklist

Follow-up Work (out of scope for this PR)

Add a supertest-based integration test for GET /metrics verifying Prometheus format and auth gating
Add Prometheus alerting rules in docs/prometheus-alerts.yml (e.g. high 5xx rate, high P95 latency)
Add METRICS_TOKEN to the CI backend/.env.example and GitHub Actions secrets documentation
Consider moving /metrics above the global rate limiter for operators who scrape at sub-15s intervals

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