Varnish Cache

Monitor Varnish Cache — cache hit ratio, backend connections, request rates, and object counts — using varnish_exporter.

Pattern: varnish_exporter → Prometheus scrape → xScaler remote_write

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Prerequisites

• Varnish Cache 6.x+
• varnish_exporter binary installed on the same host as the Varnish instance
• The exporter user must have permission to run varnishstat (typically requires membership in the varnish group)

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Option A — Prometheus Exporter

Start varnish_exporter on the Varnish host:

varnish_exporter --web.listen-address :9131

Configure Prometheus to scrape and forward to xScaler:

scrape_configs:
  - job_name: varnish
    static_configs:
      - targets: ["localhost:9131"]

remote_write:
  - url: https://euw1-01.m.xscalerlabs.com/api/v1/push
    authorization:
      credentials: <token>
    headers:
      X-Scope-OrgID: <tenant-id>

---

Option B — Grafana Alloy

prometheus.scrape "varnish" {
  targets = [{ __address__ = "localhost:9131" }]
  forward_to = [prometheus.remote_write.xscaler.receiver]
}

prometheus.remote_write "xscaler" {
  endpoint {
    url = "https://euw1-01.m.xscalerlabs.com/api/v1/push"
    authorization {
      type        = "Bearer"
      credentials = "<token>"
    }
    headers = { "X-Scope-OrgID" = "<tenant-id>" }
  }
}

---

Option C — OpenTelemetry Collector

receivers:
  prometheus:
    config:
      scrape_configs:
        - job_name: varnish
          static_configs:
            - targets: ["localhost:9131"]

processors:
  memory_limiter:
    check_interval: 1s
    limit_mib: 256
  batch:
    timeout: 10s

exporters:
  otlphttp/xscaler:
    endpoint: https://euw1-01.m.xscalerlabs.com
    headers:
      Authorization: "Bearer <token>"
      X-Scope-OrgID: "<tenant-id>"
    compression: gzip

service:
  pipelines:
    metrics:
      receivers:  [prometheus]
      processors: [memory_limiter, batch]
      exporters:  [otlphttp/xscaler]

---

Logs

Collect Varnish HTTP access log via varnishncsa. Add the following to your Alloy config:

local.file_match "varnish_logs" {
  path_targets = [{
    __address__ = "localhost",
    __path__    = "/var/log/varnish/varnishncsa.log",
    instance    = constants.hostname,
    job         = "integrations/varnish",
  }]
}

loki.source.file "varnish_logs" {
  targets    = local.file_match.varnish_logs.targets
  forward_to = [loki.write.xscaler.receiver]
}

loki.write "xscaler" {
  endpoint {
    url = "https://euw1-01.l.xscalerlabs.com/api/v1/logs/push"

    http_client_config {
      authorization {
        type        = "Bearer"
        credentials = env("XSCALER_TOKEN")
      }
    }

    headers = { "X-Scope-OrgID" = env("XSCALER_TENANT_ID") }
  }
}

Key metrics

Metric	Description
varnish_main_cache_hit	Cumulative cache hit count
varnish_main_cache_miss	Cumulative cache miss count
varnish_main_backend_conn	Total successful backend connections established
varnish_main_client_req	Total client requests received
varnish_sma_g_bytes	Bytes currently allocated in the shared memory allocator
varnish_main_threads	Current number of active worker threads