DevContainer User
54 lines
2.3 KiB
Markdown
54 lines
2.3 KiB
Markdown
# ADR 005: Prometheus Metrics via Pod Proxy
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**Status**: Accepted
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**Date**: 2026-03-05
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**Deciders**: Development Team
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---
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## Context
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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:
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- **Query a Prometheus server** — Requires Prometheus to be installed in the cluster
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- **Scrape the pod directly via Kubernetes pod proxy** — No additional dependencies
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- **Use a metrics aggregation service** — Requires additional infrastructure
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---
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## Decision
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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.
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---
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## Consequences
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- ✅ Works without Prometheus server installed — no additional infrastructure dependency
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- ✅ Direct from source with no aggregation delay — metrics are always current
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- ✅ Leverages existing Kubernetes API authentication and authorization
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- ✅ No additional service dependencies to configure or maintain
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- ⚠️ Custom Prometheus text format parser to maintain — mitigated by the parser being well-tested
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- ⚠️ Only gets metrics from one pod at a time (no aggregation across replicas) — acceptable since CSI controller typically runs one replica
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- ⚠️ No historical data (point-in-time only) — users needing historical trends should use a full Prometheus setup
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---
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## Alternatives Considered
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1. **Query Prometheus server via service proxy** (like the intel-gpu plugin) — Rejected. Would require Prometheus to be installed, adding a hard infrastructure dependency.
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2. **Use a metrics library (prom-client) for parsing** — Rejected. Adds a runtime dependency for a relatively simple parsing task.
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3. **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.
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---
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## Changelog
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| Date | Change |
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|------|--------|
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| 2026-03-05 | Initial decision |
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