CertWatch vs Prometheus Blackbox Exporter

The Hidden Cost of "Free"

Prometheus Blackbox Exporter is the industry standard for self-hosted endpoint probing. It's free, open-source, and already running in most Kubernetes clusters.

But "free" has a hidden price tag: your engineering time.

Setting up SSL certificate monitoring with Blackbox Exporter requires:

1. Configuring blackbox.yml with TLS probe modules
2. Defining targets in prometheus.yml with complex relabeling
3. Writing PromQL queries for certificate expiration
4. Setting up AlertManager with routing rules
5. Building (or finding) Grafana dashboards
6. Maintaining all of the above through upgrades

Your SREs have better things to do than debug scrape configs.

Configuration Complexity: A Tale of Two YAMLs

Blackbox Exporter Setup (The Full Stack)

Step 1: blackbox.yml

modules:
  http_2xx_ssl:
    prober: http
    timeout: 5s
    http:
      valid_http_versions: ["HTTP/1.1", "HTTP/2.0"]
      valid_status_codes: [200]
      method: GET
      tls_config:
        insecure_skip_verify: false
  tcp_tls:
    prober: tcp
    timeout: 5s
    tcp:
      tls: true
      tls_config:
        insecure_skip_verify: false

Step 2: prometheus.yml (with relabeling magic)

scrape_configs:
  - job_name: 'blackbox-ssl'
    metrics_path: /probe
    params:
      module: [http_2xx_ssl]
    static_configs:
      - targets:
        - https://api.example.com
        - https://dashboard.example.com
        - https://postgres.internal:5432
    relabel_configs:
      - source_labels: [__address__]
        target_label: __param_target
      - source_labels: [__param_target]
        target_label: instance
      - target_label: __address__
        replacement: blackbox-exporter:9115

Step 3: AlertManager rules

groups:
  - name: ssl-expiry
    rules:
      - alert: SSLCertExpiringSoon
        expr: probe_ssl_earliest_cert_expiry - time() < 86400 * 30
        for: 10m
        labels:
          severity: warning
        annotations:
          summary: "SSL certificate expiring in < 30 days"
          description: "{{ $labels.instance }} expires in {{ $value | humanizeDuration }}"

      - alert: SSLCertExpiryCritical
        expr: probe_ssl_earliest_cert_expiry - time() < 86400 * 7
        for: 5m
        labels:
          severity: critical
        annotations:
          summary: "SSL certificate expiring in < 7 days"

Step 4: Grafana Dashboard (50+ lines of JSON, or hunt for a community dashboard that may be outdated)

Step 5: AlertManager routing (more YAML for Slack/PagerDuty integration)

CertWatch Setup (The Entire Stack)

certwatch.yaml

api_key: ${CERTWATCH_API_KEY}
agent:
  name: production-cluster

endpoints:
  - address: api.example.com:443
  - address: dashboard.example.com:443
  - address: postgres.internal:5432
    protocol: tls

check_interval: 5m

Deploy:

cw-agent init  # Interactive wizard generates the config
cw-agent run   # That's it. Dashboard and alerts are automatic.

Time to value:

• Blackbox Exporter: Hours to days
• CertWatch: Minutes

The "Silent Failure" Problem

This is the most dangerous weakness of Prometheus-based monitoring.

How Prometheus Fails Silently

Prometheus uses a "pull" model—it scrapes metrics from exporters. If something breaks in that chain:

The dangerous part: In many Grafana dashboards, a missing metric looks identical to a healthy state. The panel shows "No data" or falls back to the last known value. Unless you've explicitly configured:

- alert: BlackboxExporterDown
  expr: absent(probe_success{job="blackbox-ssl"})
  for: 5m

...your monitoring system can fail without anyone noticing. Your certificates expire, alerts never fire, and you find out from customers.

How CertWatch Handles This

CertWatch uses a "push" model with heartbeat detection:

1. The cw-agent pushes data outbound to CertWatch
2. CertWatch expects regular check-ins (default: every 30 seconds)
3. If an agent goes silent, CertWatch triggers an "Agent Offline" alert

🚨 Alert: Agent "production-cluster" offline
Last seen: 5 minutes ago
Expected check-in: Every 30 seconds

Action required: Verify agent is running in your cluster.

This "watch the watcher" capability is built-in. With Prometheus, you have to architect it yourself—and most teams don't.

Feature Comparison

"But We Already Have Prometheus..."

Great! The cw-agent is designed to complement your Prometheus stack, not replace it.

Keep Your Existing Dashboards

The agent exposes a /metrics endpoint with Prometheus-compatible metrics:

# HELP certwatch_certificate_expiry_seconds Seconds until certificate expires
# TYPE certwatch_certificate_expiry_seconds gauge
certwatch_certificate_expiry_seconds{endpoint="api.example.com:443"} 2592000

# HELP certwatch_certificate_chain_valid Whether the certificate chain is valid
# TYPE certwatch_certificate_chain_valid gauge
certwatch_certificate_chain_valid{endpoint="api.example.com:443"} 1

You can scrape these metrics into your existing Prometheus and keep your Grafana dashboards. But now:

• Alerting is handled by CertWatch (no AlertManager config)
• Silent failure detection is automatic
• You get deeper certificate insights (chain, revocation, crypto strength)

Best of both worlds: Prometheus metrics for your dashboards + CertWatch alerts for reliability.

Total Cost of Ownership

Let's calculate the real cost of "free" Blackbox Exporter:

Blackbox Exporter TCO

CertWatch TCO

Even after beta pricing ends, CertWatch will cost a fraction of the engineering time Blackbox Exporter demands.

Migration Path: Blackbox Exporter → CertWatch

Step 1: Export Your Current Targets

If you have targets in prometheus.yml, extract them:

grep -A 100 'job_name.*blackbox' prometheus.yml | grep 'https://'

Step 2: Create certwatch.yaml

api_key: ${CERTWATCH_API_KEY}
agent:
  name: production-cluster

endpoints:
  # Paste your endpoints here
  - address: api.example.com:443
  - address: dashboard.example.com:443

  # For non-HTTPS TLS endpoints (databases, etc.)
  - address: postgres.internal:5432
    protocol: tls

check_interval: 5m

Step 3: Deploy the Agent

# Kubernetes (alongside your existing Prometheus)
helm repo add certwatch https://charts.certwatch.app
helm install cw-agent certwatch/cw-agent \
  --set agent.apiKey=$CERTWATCH_API_KEY \
  -f certwatch-values.yaml

# Or Docker
docker run -d \
  -e CERTWATCH_API_KEY=$CERTWATCH_API_KEY \
  -v ./certwatch.yaml:/app/certwatch.yaml \
  ghcr.io/certwatch-app/cw-agent:latest

Step 4: (Optional) Keep Prometheus Metrics

Scrape the agent's /metrics endpoint to keep your existing dashboards:

# Add to prometheus.yml
scrape_configs:
  - job_name: 'certwatch-agent'
    static_configs:
      - targets: ['cw-agent:9090']

Step 5: Retire AlertManager SSL Rules

Once CertWatch alerts are flowing to Slack/PagerDuty, you can safely remove your SSL-specific AlertManager rules.

For Teams Already Invested in Prometheus

We understand you've built expertise around Prometheus. CertWatch isn't asking you to abandon that investment:

The cw-agent fits naturally into your Kubernetes cluster alongside Prometheus. It's not either/or—it's AND.

FAQ

Does CertWatch replace Prometheus?

No. CertWatch replaces Blackbox Exporter + AlertManager + Grafana dashboards for SSL monitoring only. Keep Prometheus for everything else.

Can I still see metrics in Grafana?

Yes! The agent exposes Prometheus-compatible metrics at /metrics. Scrape them into your existing Prometheus.

What about our existing AlertManager rules?

You can keep them as backup, but CertWatch's alerting is more reliable (push model + heartbeat detection). Most teams retire their SSL AlertManager rules after validating CertWatch.

Is the agent open-source?

Yes! The cw-agent is fully open-source at github.com/certwatch-app/cw-agent. You can audit the code, contribute, or fork it.

How does this compare to writing better PromQL?

Even perfect PromQL can't solve silent failures from the pull model. And PromQL can't check certificate revocation or analyze cipher strength. The Blackbox Exporter simply doesn't expose those metrics.

The Bottom Line

Stop writing PromQL. Start monitoring.

Ready to Reclaim Your Engineering Time?

Start Free Trial →

• Deploy alongside Prometheus in minutes
• Keep your Grafana dashboards (scrape /metrics)
• Get reliable alerts without AlertManager config
• Free during beta

Last updated: January 2026. We respect Prometheus—it's excellent software. This comparison focuses specifically on SSL certificate monitoring use cases.