Prometheus Metrics

NORA exposes Prometheus-compatible metrics at the /metrics endpoint. No authentication is required.

curl http://localhost:4000/metrics

HTTP metrics

Metric	Type	Labels	Description
`nora_http_requests_total`	Counter	`registry`, `method`, `status`	Total HTTP requests processed
`nora_http_request_duration_seconds`	Histogram	`registry`, `method`	Request latency (buckets: 1ms to 10s)

The registry label is derived from the request path:

Path prefix	Label
`/v2*`	`docker`
`/npm*`	`npm`
`/simple`, `/packages`	`pypi`
`/maven2*`	`maven`
`/cargo*`	`cargo`
`/go/*`	`go`
`/raw/*`	`raw`
`/gems/*`	`gems`
`/terraform/*`	`terraform`
`/ansible/*`	`ansible`
`/nuget/*`	`nuget`
`/pub/*`	`pub`
`/conan/*`	`conan`
`/ui*`	`ui`
(other paths)	`other`

Cache metrics

Metric	Type	Labels	Description
`nora_cache_requests_total`	Counter	`registry`, `result`	Cache lookups (`hit` or `miss`)

Storage metrics

Metric	Type	Labels	Description
`nora_storage_operations_total`	Counter	`operation`, `status`	Storage operations (`get`, `put`, `delete`, `list`) with `ok` or `error` status
`nora_artifacts_total`	Gauge	`registry`	Artifacts currently stored per registry (rises and falls with GC)
`nora_storage_bytes`	Gauge	`registry`	Stored artifact bytes per registry (label `total` = full footprint incl. metadata)
`nora_storage_get_bytes`	Histogram	`registry`	Body size of buffered `Storage::get()` reads (buckets: 1KB to 512MB)
`nora_storage_verify_duration_seconds`	Histogram	`registry`	SHA-256 integrity-verify wall-clock per buffered get, including blocking-pool queue time

Circuit breaker metrics

Available when NORA_CB_ENABLED=true.

Metric	Type	Labels	Description
`nora_circuit_breaker_state`	Gauge	`registry`	Current state: `0` = closed, `1` = open, `2` = half-open
`nora_circuit_breaker_rejections_total`	Counter	`registry`	Requests rejected by an open breaker

Garbage collection metrics

Metric	Type	Description
`nora_gc_blobs_removed_total`	Counter	Orphaned blobs removed by GC
`nora_gc_bytes_freed_total`	Counter	Bytes freed by GC
`nora_gc_duration_seconds`	Histogram	Duration of GC runs (buckets: 0.1s to 300s)
`nora_gc_last_run_timestamp`	Gauge	Unix timestamp of last GC run
`nora_gc_metadata_phantoms_total`	Counter	Phantom version entries cleaned from metadata
`nora_gc_stat_failures_total`	Counter	Orphans GC could not `stat` (kept, age unknown) — nonzero means GC may be unable to reclaim space; alert on it

Retention metrics

Metric	Type	Description
`nora_retention_versions_deleted_total`	Counter	Versions removed by retention policies
`nora_retention_bytes_freed_total`	Counter	Bytes freed by retention
`nora_retention_duration_seconds`	Histogram	Duration of retention runs (buckets: 0.1s to 300s)
`nora_retention_last_run_timestamp`	Gauge	Unix timestamp of last retention run

Traffic metrics

Metric	Type	Labels	Description
`nora_downloads_total`	Counter	`registry`	Total artifact downloads
`nora_uploads_total`	Counter	`registry`	Total artifact uploads

Upstream proxy metrics

Emitted on the proxy path when NORA fetches from a configured upstream.

Metric	Type	Labels	Description
`nora_upstream_request_duration_seconds`	Histogram	`registry`, `status`	Upstream proxy request latency (buckets: 1ms to 30s)
`nora_proxy_active_downloads`	Gauge	(none)	Docker blob proxy downloads currently streaming
`nora_proxy_download_bytes_total`	Counter	(none)	Total bytes downloaded from upstream Docker registries (verified downloads only)

Revalidation & coalescing metrics

Conditional-request (304) revalidation and single-flight request coalescing on the proxy path.

Metric	Type	Labels	Description
`nora_proxy_upstream_304_total`	Counter	`registry`	Upstream `304 Not Modified` responses on revalidation
`nora_proxy_revalidation_bytes_saved_total`	Counter	`registry`	Body bytes not re-downloaded thanks to a 304 revalidation
`nora_proxy_revalidation_errors_total`	Counter	`registry`	Revalidation attempts that fell back to a full fetch
`nora_proxy_coalesced_total`	Counter	`registry`	Follower requests served from the single-flight leader without an upstream fetch
`nora_proxy_inflight`	Gauge	`registry`	Distinct keys currently being fetched under single-flight coalescing
`nora_proxy_coalesce_fallthrough_total`	Counter	`registry`, `reason`	Followers that fell through to their own fetch instead of coalescing (`reason` ∈ `leader`, `budget`)

Curation metrics

Metric	Type	Labels	Description
`nora_curation_decisions_total`	Counter	`decision`	Curation decisions by effective outcome (`allow`, `block`, `audit`, `skip`)
`nora_quarantine_holds_total`	Counter	`registry`, `outcome`	Artifacts held by the digest quarantine (`outcome` ∈ `blocked`, `observed`)

Security metrics

Metric	Type	Labels	Description
`nora_auth_namespace_scope_total`	Counter	`provider`, `decision`	OIDC `namespace_scope` enforcement decisions (`allow`, `deny`, `would_deny`)
`nora_response_upstream_url_leak_total`	Counter	`registry`	Upstream hostname detected in an outgoing response body
`nora_leak_detection_skipped_total`	Counter	`reason`	Leak-detection scans skipped (body too large or unknown size)

Integrity metrics

Metric	Type	Labels	Description
`nora_cache_write_errors_total`	Counter	`registry`, `operation`	Cache write failures in background cache tasks
`nora_metadata_corrupt_total`	Counter	`registry`	Corrupt metadata detected during publish (parse failure on existing data)

Process metrics

Metric	Type	Labels	Description
`nora_uptime_seconds`	Gauge	(none)	Process uptime in seconds

Grafana example

# Request rate by registry (5m window)
sum by (registry) (rate(nora_http_requests_total[5m]))

# Cache hit ratio
sum(rate(nora_cache_requests_total{result="hit"}[5m]))
/
sum(rate(nora_cache_requests_total[5m]))

# p99 latency per registry
histogram_quantile(0.99, sum by (le, registry) (rate(nora_http_request_duration_seconds_bucket[5m])))

# Circuit breaker alerts (open state)
nora_circuit_breaker_state == 1

# GC bytes freed per hour
increase(nora_gc_bytes_freed_total[1h])

Scrape configuration

scrape_configs:
  - job_name: nora
    scrape_interval: 15s
    static_configs:
      - targets: ['nora:4000']
    metrics_path: /metrics