DevContainer User
2.3 KiB
ADR 005: Prometheus Metrics via Pod Proxy
Status: Accepted
Date: 2026-03-05
Deciders: Development Team
Context
The plugin displays CSI driver metrics (operation latencies, error rates, volume stats). The CSI driver pods expose a Prometheus metrics endpoint on port 8080 in the standard text exposition format. The plugin needs to fetch and parse these metrics. Options:
- Query a Prometheus server — Requires Prometheus to be installed in the cluster
- Scrape the pod directly via Kubernetes pod proxy — No additional dependencies
- Use a metrics aggregation service — Requires additional infrastructure
Decision
Fetch metrics directly from the CSI driver pod's /metrics endpoint via Kubernetes pod proxy (ApiProxy.request to /api/v1/namespaces/{ns}/pods/{pod}:8080/proxy/metrics). Parse the Prometheus text exposition format in-browser using a custom parser in metrics.ts. No dependency on a Prometheus server installation.
Consequences
- ✅ Works without Prometheus server installed — no additional infrastructure dependency
- ✅ Direct from source with no aggregation delay — metrics are always current
- ✅ Leverages existing Kubernetes API authentication and authorization
- ✅ No additional service dependencies to configure or maintain
- ⚠️ Custom Prometheus text format parser to maintain — mitigated by the parser being well-tested
- ⚠️ Only gets metrics from one pod at a time (no aggregation across replicas) — acceptable since CSI controller typically runs one replica
- ⚠️ No historical data (point-in-time only) — users needing historical trends should use a full Prometheus setup
Alternatives Considered
-
Query Prometheus server via service proxy (like the intel-gpu plugin) — Rejected. Would require Prometheus to be installed, adding a hard infrastructure dependency.
-
Use a metrics library (prom-client) for parsing — Rejected. Adds a runtime dependency for a relatively simple parsing task.
-
JSON metrics endpoint instead of Prometheus format — Rejected. The CSI driver only exposes Prometheus text format; a JSON endpoint would require changes to the driver itself.
Changelog
| Date | Change |
|---|---|
| 2026-03-05 | Initial decision |