How to Test Your App Against a CDN or DNS Provider Failure: Chaos Engineering Exercises

Runbook validation checklist:

• Can you update NS/A/CNAME records automatically under the same RPO constraints?
• Do your clients handle DNS lookup failures gracefully (exponential backoff, cached data, or alternate hostnames)?
• Is the status page and incident communication reachable on a non-affected domain?

3) Block Cloudflare edge IP ranges (egress partition)

Goal: Simulate a network partition between your cluster/region and Cloudflare by dropping egress traffic to Cloudflare's IP ranges.

Blast radius: Medium. Use staging first or a single AZ.

Tools: ipset + iptables on nodes, Chaos Mesh network-loss emulation for Kubernetes.

1. Gather Cloudflare's IP ranges (published on their site) or use your CDN's IP set.
2. Create an ipset and add the ranges, then apply iptables DROP for egress to that set.
3. Run traffic and confirm the CDN is unreachable from the blocked environment while logs show connection errors to the CDN.
4. Validate fallback routing: does traffic automatically route to a secondary CDN or origin-direct endpoint?

sudo ipset create cfset hash:net
# Add ranges (example)
sudo ipset add cfset 173.245.48.0/20
sudo iptables -I OUTPUT -m set --match-set cfset dst -j DROP
# Rollback:
sudo iptables -D OUTPUT -m set --match-set cfset dst -j DROP
sudo ipset destroy cfset

Runbook validation checklist:

• Network ops quickly removed the block or activated the documented mitigation.
• Traffic shifted to the planned path (multi-CDN, origin-direct, or degraded mode).
• Alerts included the correct network diagnostics and runbook steps.

4) TLS handshake / certificate-related failures

Goal: Simulate TLS handshake failures at the edge: mismatched ALPN (HTTP/2 vs HTTP/3), revoked certs, or incorrect SNI handling by the CDN.

Blast radius: Medium. Can silently break clients with strict TLS policies.

1. Using a Toxiproxy or a custom test endpoint, present an invalid certificate or refuse the TLS handshake for a region/canary.
2. Run clients with different TLS stacks (modern browsers, curl with different versions, mobile SDKs) and observe behavior.
3. Check whether your fallback path uses alternate TLS config or plain HTTP on a status subdomain.

Runbook validation checklist:

• Does the incident page use a certificate not dependent on the CDN?
• Are operators able to instruct clients or provide temporary cert pin updates if needed?

5) WAF or rate-limit induced blocking (edge policy misfire)

Goal: Validate detection and remediation when a WAF rule or CDN rate-limit starts returning 403/429 for legitimate traffic.

Blast radius: Low-to-high depending on rule scope.

1. Simulate WAF blocks by injecting blocked headers or payload patterns from test clients and confirm WAF logs the matches.
2. Automate toggling of a rule via CDN API (if supported) as part of your runbook and measure time to lift the block.
3. Confirm web app and API clients recover after the rule is relaxed.

Runbook validation checklist:

• WAF rules are identifiable and reversible via API within SLAs.
• Escalation flows include security owners for rule changes and approvals.

Automation patterns for real drills

Your runbook is only as good as how quickly you can execute it. Automate the manual steps and test the automation during your drills.

DNS failover automation example (Terraform + provider API)

Use Terraform to flip an A/CNAME from the primary zone to a backup host. Keep the following pattern in your repo:

# Pseudo Terraform workflow
# 1) Use a short TTL record for the canary
data "dns_record" "current" {}
resource "dns_record" "app" {
  name = "app.example.com"
  ttl  = 60
  value = var.primary_ip
}
# During a failover, update var.primary_ip to backup

Integrate this with a GitHub Actions runbook job that requires two approvals in prod. The automation should also verify via dig and HTTP that the new target has begun serving traffic before marking the incident as mitigated. See the cloud pipelines case study for patterns that scale.

Multi-CDN active-active tests

If you run multi-CDN, create canary headers that route 5% of traffic to CDN-B. Use chaos to break CDN-A's edges and measure how quickly traffic weights adjust and if stateful sessions survive. For edge orchestration patterns, see edge orchestration and security guides.

Observability and test assertions

For every experiment, collect these signals automatically and assert on them to evaluate resilience:

• DNS resolution success rate and latency per resolver
• HTTP status distribution (2xx/3xx/4xx/5xx) split by edge vs origin
• End-to-end latency percentiles (p50/p95/p99)
• Error budget burn rate for the service during the experiment
• Runbook time-to-first-action and time-to-mitigation

Decide where logs and synthetic results will live — durable options range from object stores to network‑attached storage for recordings; consider a Cloud NAS for on-prem or studio-style archive of drill recordings.

Common failure patterns and mitigations — checklist for your runbook

• DNS fails — mitigation: short TTLs, pre-configured secondary DNS provider, automation to change NS or A/CNAME records, ensure domain has delegation to backup provider.
• CDN edge returns 5xx — mitigation: origin-direct path with strict auth and IP allowlist, static status site on S3/Netlify cached by an alternative CDN, or failover CDN.
• TLS issues — mitigation: host status pages on a different provider with separate cert chain, keep ACME/renewal automation separate from the CDN-managed certs.
• WAF/rate-limits — mitigation: allowlist internal health-check IPs, provide emergency toggle with guardrails and approvals.
• Edge compute misconfig — mitigation: ensure origin replicas or a fallback route avoid depending on edge-only logic. For compliance‑first edge patterns, see serverless edge compliance.

2026 trends to bake into your strategy

The industry in 2026 is moving faster toward more complex edge features and more consequential edge failure modes. Key trends to incorporate in your chaos program:

• Multi-DNS & multi-CDN are standard. Single-vendor DNS or CDN dependency is increasingly considered a risk for any high-availability app.
• Edge compute & functions means business logic is sometimes executed at the CDN. Ensure critical flows also work when edge compute is unavailable. See serverless edge design notes at Serverless Edge for Compliance-First Workloads.
• HTTP/3 and QUIC adoption changes handshake and error modes. Test across protocol stacks.
• Infrastructure as runbook — programmatic, audited, and tested automation (GitOps) for DNS/CDN changes is now a best practice.

Post-drill: how to run a useful blameless postmortem

1. Collect all logs, synthetic checks, and recordings from the incident channel.
2. Compare runbook expected steps vs actual actions and timings.
3. Identify missing automation or unclear owner handoffs and convert them into prioritized work items. See lessons on triage and converting game-bug workflows into enterprise fixes in the bounty triage case study.
4. Update your runbook and automation repository; then re-run the test to verify the fix.

"You can't rely on a single ground truth at the edge. Test your fallbacks early and often — and make your runbooks executable like code." — Practical SRE mantra for 2026

Actionable checklist to run this week

1. Inventory your DNS and CDN providers and validate secondary options exist for each critical domain.
2. Set short TTLs for critical records in staging and prepare Terraform runbooks to flip records automatically.
3. Implement a canary traffic header and route 1-5% of traffic to a failover path; verify session affinity and statefulness. Consider canary header patterns described in edge & streaming orchestration guides.
4. Practice the CDN 5xx and DNS SERVFAIL experiments in staging with synthetic checks and time-authorized drills.
5. Document and automate rollback steps; add approval gates for production change jobs.

Final takeaways

Edge and DNS failures are no longer edge cases — they're part of the reliability landscape in 2026. A well-designed chaos program focused on CDN-level and DNS failure modes will validate both your technical fallbacks and your incident runbooks. The experiments here give you a pragmatic path from simple, low-risk tests to realistic production drills that reveal gaps you can fix before they impact customers.

Call to action

Ready to run a disaster drill this week? Start with the DNS SERVFAIL experiment in a staging environment and use the Terraform automation template in your repo. If you want ready-to-run scripts and a Kubernetes Chaos Mesh manifest tailored for Cloudflare-IP blocking, download the companion lab bundle and step-by-step checklist from our site, or subscribe for the weekly SRE lab guide that walks you through each experiment with code and observability dashboards.

Related Reading

• Preparing SaaS and Community Platforms for Mass User Confusion During Outages
• Serverless Edge for Compliance-First Workloads — A 2026 Strategy
• Edge Orchestration and Security for Live Streaming in 2026
• Field Report: Hosted Tunnels, Local Testing and Zero‑Downtime Releases — Ops Tooling
• Case Study: How Data-Driven IP Discovery Can Turn a Motif into a Franchise
• Bungie’s Marathon: What the New Previews Reveal About Story, Mechanics, and Destiny DNA
• Pod: 'Second Screen' Presidency — How Presidents Manage Multiple Platforms
• How Digital PR and Social Search Create Authority Before Users Even Search
• When Agentic AIs Meet QPUs: Orchestrating Hybrid Workflows Without Breaking Things