APM Gateway

apm-gateway is a stateless Prometheus façade for application performance monitoring. It executes PromQL queries for request rates, latency percentiles, and error rates and returns structured JSON. No database — all metrics live in Prometheus.

Prometheus Queries

Endpoint	PromQL
GET /api/v1/services/metrics	sum by (app, namespace) (rate(http_requests_total[5m]))
GET /api/v1/endpoints/slowest	topk(10, histogram_quantile(0.99, sum by (le, handler, method) (rate(http_request_duration_seconds_bucket[5m]))))
GET /api/v1/endpoints/erroring	topk(10, sum by (handler, method) (rate(http_requests_total{status=~"5.."}[5m])))

These queries follow the OpenMetrics conventions used by Prometheus client libraries, Istio service mesh metrics, and most Kubernetes-native application frameworks.

REST API

Method	Path	Description
GET	/api/v1/services/metrics	Request rate per service (?namespace=)
GET	/api/v1/endpoints/slowest	Top 10 endpoints by p99 latency
GET	/api/v1/endpoints/erroring	Top 10 endpoints by 5xx error rate
GET	/healthz	Health check

Metric Labels

The queries expect these standard labels on http_requests_total and http_request_duration_seconds:

• app or service — workload name
• namespace — Kubernetes namespace
• handler — route or endpoint path
• method — HTTP method
• status — HTTP status code

If your workloads use non-standard label names (e.g. Istio uses destination_service_name), update the PromQL in the handler or proxy the queries through a Prometheus recording rule.

Environment Variables

Variable	Default	Description
PROMETHEUS_URL	http://localhost:9090	Prometheus endpoint
PORT	8101	HTTP port