How to configure Web Application Firewalls (WAF) to mitigate volumetric DDoS attacks in cloud environments?

Enable the WAF's rate‑limit and anomaly‑detection modules, then tune per‑endpoint thresholds to block traffic that exceeds normal baselines.

Steps

1. Profile baseline traffic – Use CloudWatch metrics (AWS), Azure Monitor, or GCP Monitoring for 7‑day average request rate per URI. Example baseline: 120 rps for /api/*.
2. Create a rate‑based rule – Set the limit slightly above baseline (e.g., 200 rps) and define a 5‑minute aggregation window.
3. Add an anomaly‑detection rule – Enable “IP reputation” and “SQLi/XSS” signatures; set the action to block for scores ≥ 5.
4. Scope the rule – Apply to the specific CloudFront distribution, Azure Front Door route, or GCP backend service.
5. Whitelist health‑check sources – Add the load‑balancer IP ranges to an allow‑list rule with priority higher than the rate rule.
6. Enable automatic mitigation – Turn on “auto‑scale protection” (AWS Shield Advanced) or “adaptive protection” (Azure) to raise limits during legitimate spikes.
7. Monitor and adjust – Set CloudWatch alarm on WAFBlockedRequests > 5 % of total; refine thresholds weekly.

Tool comparison

| Provider | Rate‑limit API | Anomaly detection | Auto‑scale flag |
|----------|----------------|-------------------|-----------------|
| AWS WAF | aws wafv2 create-rate-based-rule | Managed rule groups | EnableManagedRuleGroupStatement with AWSManagedRulesAnonymousIpList |
| Azure Front Door WAF | az network front-door waf-policy rule create --type RateLimit | ManagedRuleSet | policySettings.enableAutoTune=true |
| GCP Cloud Armor | gcloud compute security-policies rules create --expression="request.rate < 200" | preconfigured-waf | adaptiveProtectionConfig.enabled=true |

Example CLI snippets

# AWS CLI – rate‑based rule
aws wafv2 create-rate-based-rule \
  --name high‑rate‑api \
  --scope REGIONAL \
  --metric-name HighRateAPI \
  --rate-key IP \
  --rate-limit 200 \
  --visibility-config SampledRequestsEnabled=true,CloudWatchMetricsEnabled=true,MetricName=HighRateAPI

# Azure CLI – rate limit rule
az network front-door waf-policy rule create \
  --policy-name prodWaf \
  --resource-group rg-prod \
  --name apiRateLimit \
  --priority 100 \
  --action Block \
  --type RateLimit \
  --rate-limit-threshold 200 \
  --rate-limit-duration 5

Gotcha: Aggressive limits can drop legitimate burst traffic from autoscaling pods; always whitelist health‑check IPs and keep a low‑priority “bypass” rule for known CDN edge ranges.