Prometheus Metrics

PRISM exports metrics in Prometheus text exposition format on the admin API at GET /metrics.

Request Metrics

Metric	Type	Description
prism_requests_total{status="hit|miss|bypass|stale|error"}	counter	Total requests by cache status
prism_inflight_requests	gauge	Currently processing requests
prism_rate_limit_rejections_total	counter	Requests rejected by rate limiter (429)

Render Metrics

Metric	Type	Description
prism_render_active	gauge	Currently active renders
prism_render_queue_depth	gauge	Requests waiting for a Chrome tab
prism_render_total	counter	Total renders completed
prism_render_duration_ms	histogram	Render duration in milliseconds
prism_shadow_renders_total	counter	Shadow renders completed (shadow mode)
prism_content_validation_failures_total	counter	Renders that failed content validation

prism_render_duration_ms histogram buckets: 100, 250, 500, 1000, 2500, 5000, 10000, 30000

Cache Metrics

Metric	Type	Description
prism_cache_entries	gauge	Number of entries in the render cache
prism_cache_memory_bytes	gauge	Memory used by cached entries
prism_cache_evictions_total	counter	Cache entries evicted (LRU or TTL)

Chrome Tab Pool Metrics

Metric	Type	Description
prism_tab_pool_size	gauge	Total tabs in the pool
prism_tab_pool_available	gauge	Idle tabs available for rendering
prism_tab_crashes_total	counter	Tab crashes detected
prism_tab_creates_total	counter	New tabs created
prism_tab_recycles_total	counter	Tabs recycled after max renders
prism_chrome_restarts_total	counter	Full Chrome process restarts

Origin Metrics

Metric	Type	Description
prism_origin_requests_total	counter	Requests forwarded to the origin server
prism_origin_duration_sum_ms	counter	Cumulative origin request duration (ms)

Warmup Metrics

Metric	Type	Description
prism_warmup_urls_processed	counter	URLs successfully warmed up
prism_warmup_urls_failed	counter	URLs that failed during warmup

Circuit Breaker

Metric	Type	Description
prism_circuit_breaker_state	gauge	0 = closed (healthy), 1 = open (tripped), 2 = half-open (probing)

System Metrics

Metric	Type	Description
prism_uptime_seconds	gauge	Seconds since PRISM started
process_resident_memory_bytes	gauge	Resident memory (RSS) of the PRISM process
process_virtual_memory_bytes	gauge	Virtual memory of the PRISM process
process_cpu_seconds_total	counter	Total CPU time consumed
process_open_fds	gauge	Open file descriptors
process_max_fds	gauge	Maximum file descriptors (ulimit)
process_threads	gauge	Number of OS threads

---

Scrape Configuration

Add PRISM to your Prometheus scrape_configs:

scrape_configs:
  - job_name: prism
    scrape_interval: 15s
    static_configs:
      - targets: ['127.0.0.1:4001']
    # If bearer_token is configured:
    authorization:
      type: Bearer
      credentials: your-secret-token

---

Grafana Dashboard

Import this JSON snippet as a Grafana dashboard to get started with key panels:

{
  "title": "Trident PRISM",
  "panels": [
    {
      "title": "Cache Hit Rate",
      "type": "stat",
      "targets": [
        {
          "expr": "rate(prism_requests_total{status=\"hit\"}[5m]) / (rate(prism_requests_total{status=\"hit\"}[5m]) + rate(prism_requests_total{status=\"miss\"}[5m]))",
          "legendFormat": "Hit Rate"
        }
      ],
      "fieldConfig": {
        "defaults": { "unit": "percentunit", "thresholds": { "steps": [
          { "value": 0, "color": "red" },
          { "value": 0.7, "color": "yellow" },
          { "value": 0.9, "color": "green" }
        ]}}
      }
    },
    {
      "title": "Render Duration (p50 / p95 / p99)",
      "type": "timeseries",
      "targets": [
        {
          "expr": "histogram_quantile(0.50, rate(prism_render_duration_ms_bucket[5m]))",
          "legendFormat": "p50"
        },
        {
          "expr": "histogram_quantile(0.95, rate(prism_render_duration_ms_bucket[5m]))",
          "legendFormat": "p95"
        },
        {
          "expr": "histogram_quantile(0.99, rate(prism_render_duration_ms_bucket[5m]))",
          "legendFormat": "p99"
        }
      ],
      "fieldConfig": { "defaults": { "unit": "ms" } }
    },
    {
      "title": "Active Renders & Queue Depth",
      "type": "timeseries",
      "targets": [
        { "expr": "prism_render_active", "legendFormat": "Active" },
        { "expr": "prism_render_queue_depth", "legendFormat": "Queued" }
      ]
    },
    {
      "title": "Tab Pool",
      "type": "timeseries",
      "targets": [
        { "expr": "prism_tab_pool_size", "legendFormat": "Total" },
        { "expr": "prism_tab_pool_available", "legendFormat": "Available" }
      ]
    },
    {
      "title": "Cache Entries & Memory",
      "type": "timeseries",
      "targets": [
        { "expr": "prism_cache_entries", "legendFormat": "Entries" },
        { "expr": "prism_cache_memory_bytes", "legendFormat": "Memory (bytes)" }
      ]
    },
    {
      "title": "Circuit Breaker State",
      "type": "stat",
      "targets": [
        { "expr": "prism_circuit_breaker_state", "legendFormat": "State" }
      ],
      "fieldConfig": {
        "defaults": {
          "mappings": [
            { "type": "value", "options": { "0": { "text": "CLOSED", "color": "green" } } },
            { "type": "value", "options": { "1": { "text": "OPEN", "color": "red" } } },
            { "type": "value", "options": { "2": { "text": "HALF-OPEN", "color": "yellow" } } }
          ]
        }
      }
    },
    {
      "title": "Origin Latency (avg)",
      "type": "timeseries",
      "targets": [
        {
          "expr": "rate(prism_origin_duration_sum_ms[5m]) / rate(prism_origin_requests_total[5m])",
          "legendFormat": "Avg Origin Latency (ms)"
        }
      ],
      "fieldConfig": { "defaults": { "unit": "ms" } }
    },
    {
      "title": "Process Memory",
      "type": "timeseries",
      "targets": [
        { "expr": "process_resident_memory_bytes", "legendFormat": "RSS" },
        { "expr": "process_virtual_memory_bytes", "legendFormat": "Virtual" }
      ],
      "fieldConfig": { "defaults": { "unit": "bytes" } }
    }
  ]
}

Key Alerts

groups:
  - name: prism
    rules:
      - alert: PrismCircuitBreakerOpen
        expr: prism_circuit_breaker_state == 1
        for: 1m
        labels: { severity: critical }
        annotations:
          summary: "PRISM circuit breaker is open — renders disabled"

      - alert: PrismHighRenderLatency
        expr: histogram_quantile(0.95, rate(prism_render_duration_ms_bucket[5m])) > 10000
        for: 5m
        labels: { severity: warning }
        annotations:
          summary: "PRISM p95 render latency > 10s"

      - alert: PrismTabPoolExhausted
        expr: prism_tab_pool_available == 0
        for: 2m
        labels: { severity: warning }
        annotations:
          summary: "No available Chrome tabs in the pool"