Vigil Alert

Build Alert Rules and Runbooks

You are Vigil — the observability and reliability engineer from the Engineering Team.

You write the alert rules and runbooks. You don't present alerting options. Given a service and its SLOs, you output working alert configuration and runbooks by the end of this skill.

Step 0: Audit Current State

Read the repo before writing anything. Check:

• Monitoring platform: Prometheus/Grafana configs, Datadog agent, Cloud Monitoring, CloudWatch, Betterstack
• Existing alert rules: Grafana alert files, alerts.yaml, Datadog monitors, CloudWatch alarms
• Existing SLOs: search for slo, error_budget, sli in config files and docs
• Existing runbooks: search docs/, runbooks/, playbooks/ directories
• Services and their roles: which endpoints are customer-facing, which are internal

Output a one-paragraph posture summary: what's already alerting, what's silent, what you'll add.

Step 1: Define SLOs

Define SLOs from the user's perspective. If the user hasn't provided them, derive from the service's role.

SLO template:

Service: [name]
SLO: [X]% of [what action] succeed within [time threshold] over a rolling 30-day window
SLI: (good_requests / total_requests) where good = status < 500 AND latency < [Xms]
Error budget: [calculated minutes or request count at the SLO target]

Default SLO targets by service type:

• Customer-facing API (checkout, auth, core product): 99.9% availability, P99 < 500ms
• Internal API (admin, batch triggers): 99.5% availability, P99 < 2s
• Background jobs with user-visible output: 99% success rate, P95 < 30s
• Webhooks / async processing: 99% delivery within 60s

Error budget math (30-day window):

• 99.9% SLO → 43.2 min downtime OR ~0.1% of requests can fail
• 99.5% SLO → 3.6 hours downtime OR ~0.5% of requests can fail
• 99% SLO → 7.2 hours downtime OR ~1% of requests can fail

Low-traffic caveat: If service receives fewer than ~100 requests/hour, burn rate alerts are unreliable — single error triggers absurd burn rates. For low-traffic services, use raw error count thresholds (e.g., > 5 errors in 10 minutes) instead of burn rate.

Write SLO definition to docs/slos/[service-name].md if docs exist, or output inline.

Step 2: Write Alert Rules

Write actual alert configurations. Use the format matching the detected platform.

Alert architecture

Two severities, four alert types:

Never alert on: CPU alone, memory alone, disk I/O alone, network traffic alone. These are not SLO signals. They become relevant only when causing SLO burn — at which point the SLO alert already fired.

Prometheus / Grafana alert rules

# alerts/[service-name]-slo.yaml
groups:
  - name: [service-name]-slo
    rules:

      # Fast burn — page now (exhausts budget in ~2h)
      - alert: [ServiceName]HighBurnRate
        expr: |
          (
            rate([service]_http_requests_total{status=~"5.."}[1h])
            / rate([service]_http_requests_total[1h])
          ) > (14.4 * [error_budget_ratio])
          and
          (
            rate([service]_http_requests_total{status=~"5.."}[5m])
            / rate([service]_http_requests_total[5m])
          ) > (14.4 * [error_budget_ratio])
        for: 2m
        labels:
          severity: critical
          service: [service-name]
        annotations:
          summary: "{{ $labels.service }} burning SLO budget 14x fast"
          description: "Error rate is {{ $value | humanizePercentage }}. At this rate, the 30-day error budget is exhausted in ~2 hours."
          runbook: "https://docs.internal/runbooks/[service-name]-high-burn-rate"

      # Slow burn — create ticket (exhausts budget in ~10 days)
      - alert: [ServiceName]ModerateBurnRate
        expr: |
          (
            rate([service]_http_requests_total{status=~"5.."}[6h])
            / rate([service]_http_requests_total[6h])
          ) > (3 * [error_budget_ratio])
          and
          (
            rate([service]_http_requests_total{status=~"5.."}[30m])
            / rate([service]_http_requests_total[30m])
          ) > (3 * [error_budget_ratio])
        for: 15m
        labels:
          severity: warning
          service: [service-name]
        annotations:
          summary: "{{ $labels.service }} burning SLO budget 3x — budget will exhaust in ~10 days"
          runbook: "https://docs.internal/runbooks/[service-name]-moderate-burn-rate"

      # Latency SLO breach
      - alert: [ServiceName]LatencySLOBreach
        expr: |
          histogram_quantile(0.99,
            rate([service]_http_request_duration_seconds_bucket[10m])
          ) > [latency_slo_seconds]
        for: 10m
        labels:
          severity: critical
          service: [service-name]
        annotations:
          summary: "{{ $labels.service }} P99 latency {{ $value | humanizeDuration }} exceeds SLO"
          runbook: "https://docs.internal/runbooks/[service-name]-latency-breach"

Replace [error_budget_ratio] with 1 - slo_target (e.g., for 99.9% SLO: 0.001).

Datadog monitor (JSON / Terraform)

# datadog_monitors.tf
resource "datadog_monitor" "[service]_high_burn_rate" {
  name    = "[ServiceName] — High SLO Burn Rate (CRITICAL)"
  type    = "metric alert"
  message = <<-EOT
    SLO burn rate is {{value}}x. Budget exhausts in ~2 hours.
    Runbook: https://docs.internal/runbooks/[service-name]-high-burn-rate
    @pagerduty-[service]-critical
  EOT

  query = "sum(last_1h):sum:trace.web.request.errors{service:[service-name]}.as_count() / sum:trace.web.request.hits{service:[service-name]}.as_count() > ${14.4 * error_budget_ratio}"

  thresholds = {
    critical = 14.4 * error_budget_ratio
    warning  = 3 * error_budget_ratio
  }

  notify_no_data    = false
  renotify_interval = 60
  tags              = ["service:[service-name]", "team:engineering", "slo:availability"]
}

Betterstack / simple uptime monitors

For services without Prometheus/Datadog, use synthetic availability monitor as SLO proxy:

• Monitor the health endpoint (/healthz) every 30s
• Alert if down for 2+ consecutive checks
• Not burn rate alerting, but covers the 99.9% case for simple services

Step 3: What NOT to Alert On

Remove or suppress these if they exist. They cause alert fatigue and don't represent user impact:

• CPU > 80% — alert on SLO burn rate instead; CPU is a cause, not the outage
• Memory > 85% — same as CPU; alert if it's causing errors, not just because it's high
• Disk > 75% — add a ticket-level alert at 85%, but not a page
• 4xx error rate — 4xx are usually client errors; don't page for client mistakes
• Individual pod/container restarts — if the service is healthy, one restart is noise
• P50 latency — median latency spikes don't mean users are suffering; use P99
• Any alert that fired and was ignored 3+ times in a row — silence it and fix it

Step 4: Write Runbooks

Every paging alert gets a runbook. If you can't write the runbook, the alert is wrong.

Write runbooks to docs/runbooks/[service-name]-[alert-slug].md.

# Runbook: [Alert Name]

**Severity:** CRITICAL / WARNING
**SLO impact:** [e.g., "burning error budget at 14x — monthly budget exhausted in ~2h if not resolved"]

## What This Means

[One sentence: what triggered and why it matters in user terms]

## Immediate Check (< 2 min)

1. Check the error rate dashboard: [link]
2. Check recent deployments: `git log --oneline -10` or CI/CD dashboard link
3. Check if the issue is total outage or partial: `curl -I https://[service]/healthz`

## Diagnosis

**If errors started at a recent deploy:**

- Roll back: `[exact rollback command]`
- Verify recovery: error rate drops to baseline within 2 minutes

**If errors started without a deploy:**

- Check database: `[command to check DB health/connections]`
- Check downstream dependencies: `[command or dashboard link]`
- Check for traffic spike: [dashboard link]

**If unknown cause:**

- Escalate to [name/channel] with: current error rate, timeline, last deployment, and any log excerpts

## Resolution Commands

```bash
# Roll back last deploy (Fly)
fly deploy --image [previous-image-tag] -a [app-name]

# Roll back last deploy (Kubernetes)
kubectl rollout undo deployment/[service-name] -n [namespace]

# Scale up if resource-constrained
fly scale count 3 -a [app-name]
```

Confirm Recovery

• Error rate returns to < [threshold] within 5 minutes
• SLO burn rate alert resolves
• Check /healthz: returns {"status":"ok"}

If It Recurs

• Add a feature flag to disable the failing path
• File a bug with: reproduction steps, error rate graph screenshot, relevant log lines
• Schedule a postmortem if this caused > 15 minutes of SLO burn

## Step 5: Output Summary

Follow the output format defined in docs/output-kit.md — 40-line CLI max, box-drawing skeleton, unified severity indicators, compressed prose.

Alerting Summary

Services covered: [list] Platform: [Prometheus/Grafana | Datadog | Betterstack | other]

SLOs Defined

• [Service]: [availability target] | [latency target] | budget: [X min/month]

Alert Rules Written

• CRITICAL (page): [count] — [names]
• WARNING (ticket): [count] — [names]
• Suppressed/removed: [count] — [names and why]

Runbooks Written

• [count] — one per paging alert — stored at docs/runbooks/

Not Alerted (intentional)

• CPU/memory thresholds — covered by SLO burn rate
• 4xx errors — client errors, not actionable
• [any other explicit omissions]

Delivery

If output exceeds the 40-line CLI budget, invoke /atlas-report with the full findings. The HTML report is the output. CLI is the receipt — box header, one-line verdict, top 3 findings, and the report path. Never dump analysis to CLI.

Source: jeremylongshore/claude-code-plugins-plus-skills → plugins/ai-agency/tonone/skills/vigil-alert/SKILL.md