Incident Response Playbook for Domain and DNS Teams During a Major CDN Outage

When a CDN or DNS provider goes dark, your domain can become the single point of failure — this runbook lets domain and DNS teams move fast to contain damage, reroute traffic, and restore service with minimal churn.

Major outages in late 2025 and early 2026 (notably high-profile CDN and DNS incidents) reinforced a hard lesson: product teams assume edge providers are rock-solid until they're not. If you own domains, WHOIS, and DNS, you must own the containment plan. This playbook is a practitioner-oriented runbook for domain/DNS teams—complete with commands, communication templates, DNS swap and rollback steps, and postmortem actions.

Why DNS teams must lead CDN outage containment in 2026

Trends in 2026 make this checklist critical: CDN consolidation and edge compute centralization mean more systems now depend on fewer providers. Multi-CDN strategies are common, but many teams still have single points of failure at DNS or registry levels. Meanwhile, API-first DNS tooling, programmable edge, and stricter security controls (DNSSEC adoption and registrar locks) add both capability and complexity.

Domain/DNS teams can move faster than application teams in many outages because DNS changes can reroute traffic globally within minutes if prepared right. But those minutes require prework: API keys, scripts, secondary DNS, pre-staged records and tested rollback paths.

Pre-incident preparation (do this now)

1. Inventory — Maintain a living inventory of domains, hosted zones, registrars, DNS providers, TTLs, DS records, registrar and DNS API keys, and contact escalation paths. Store credentials in a vault with emergency access.
2. Secondary authoritative DNS — Configure a secondary/backup authoritative provider and replicate zones. For critical domains, use providers that support AXFR/IXFR or API-based sync. Test failovers quarterly.
3. Pre-warmed backup records — Publish backup A/AAAA and CNAME records (to alternate CDN or origin) in a staging namespace or with long-validity comments. Keep a pre-approved list of IPs and CNAMEs you can switch to quickly.
4. Low-TTL strategy — Decide TTL policy for failovers. Recommended pattern: default TTL 300s (5m) for critical services, with the option to drop to 30–60s during incidents. Know which records are cached by large resolvers longer than TTL.
5. DNSSEC playbook — Document how DS records are managed. When changing nameservers or providers, DNSSEC can complicate switchover. For emergency swaps, you may need to temporarily remove DS records at the registrar (with cautious rollback steps).
6. Runbook & automation — Keep IaC for DNS (Terraform, Pulumi) and emergency scripts versioned and runnable. Create tested scripts for API-driven nameserver changes, record swaps, and TTL updates. See patterns for serverless/edge automation that help with multi-provider orchestration.
7. Testing cadence — Run simulated failovers (DNS chaos days) and tabletop exercises with comms templates to reduce friction under pressure.

Incident detection & first 10 minutes (triage)

Time is the enemy. Within the first 10 minutes follow a tight triage checklist:

• Declare incident and create an incident channel (Slack, Teams, PagerDuty incident).
• Identify scope: which domains, subdomains, TLDs, and regions are affected.
• Confirm if problem is CDN, DNS, or both.
• Notify stakeholders (SRE, product, legal, comms) using the internal template below.

Quick, authoritative checks (run immediately)

Use these commands from multiple networks (office, cloud, mobile):

# Check authoritative NS
dig +short NS example.com

# Trace resolution path
dig +trace www.example.com

# Check A/AAAA/CNAME at authoritative nameserver
dig @ns1.example-dns.com www.example.com A CNAME +noall +answer

# Check CDN health via HTTP
curl -I https://www.example.com --resolve "www.example.com:443:203.0.113.10"

# WHOIS check for registrar problems
whois example.com

Interpretation tips:

• If authoritative nameservers return NXDOMAIN or SERVFAIL, the DNS provider or zone is likely broken.
• If DNS resolution is fine but HTTP returns 502/524/520, the CDN or origin path may be failing.
• If WHOIS shows registrar locks changed or nameservers unexpectedly altered, treat it as a high trust/ownership incident and escalate to registrar support & legal.

Decision matrix: DNS swap vs record swap vs origin reroute

Pick the fastest reliable option. Use this matrix:

• Authoritative DNS provider down — Perform a nameserver swap to secondary DNS (if pre-configured) or change nameservers via registrar API. Secondary DNS is fastest if it has accurate zones.
• CDN edge failure but DNS healthy — Update CNAME/A records to an alternate CDN or to origin IPs. For apex domains, use ALIAS/ANAME or A/AAAA to origin addresses.
• Both DNS and CDN unreliable — Use registrar to swap to a trusted backup DNS provider and simultaneously switch records to the origin or an alternate CDN.

Runbook: Step-by-step

Step 0 — Declare and communicate

Create an incident channel, post a first status using the template below, and assign roles: Incident Commander (IC), DNS Lead, Communications, Legal, and Escalation contact at registrar/CDN.

Step 1 — Gather canonical facts

• List affected hostnames and zones.
• List current TTLs, authoritative NS, and DNSSEC status (DS records).
• Take screenshots of provider status pages and API responses for audit.

Step 2 — Select mitigation action

Choose one of the following based on scope and provider status.

Option A — Nameserver (NS) swap to secondary authoritative

1. Validate that secondary provider has fully-synced zones and matching SOA serials.
2. If DNSSEC is enabled, evaluate DS/Signing status. If you cannot add DS quickly, consider temporarily removing DS at the registrar (and document for rollback).
3. Change nameservers at the registrar via API. Where possible use registrar API to avoid support queues. Example (AWS Route53 Registrar):

# Example: change nameservers with a registrar API (pseudo-example)
curl -X POST "https://api.registrar.example/v1/domains/example.com/nameservers" \
  -H "Authorization: Bearer $REG_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"nameservers":["ns1-backup.example-dns.com","ns2-backup.example-dns.com"]}'

Verification:

• Check the delegation via multiple global resolvers: dig +short NS example.com @8.8.8.8
• Monitor TTL expiry windows for cached NS records; propagation depends on previous NS TTL.

Option B — DNS record swap (CNAME / A / ALIAS)

1. Lower the TTL on the affected records to 30–60s if not already low. Apply on authoritative provider.
2. Swap the CNAME to an alternate CDN or update A/AAAA records to origin/load-balancer IPs.
3. Confirm HTTP responses from the new target (curl, browser checks).

# Example: update record in AWS Route53 via AWS CLI
aws route53 change-resource-record-sets \
  --hosted-zone-id Z1234567890 \
  --change-batch file://change-batch.json

# change-batch.json contains the new record set to swap CNAME/A

Option C — IP/BGP level reroute (advanced)

If you control origin IP space and Peering, coordinate with your network team or upstream provider to announce prefixes via BGP from an alternate AS or PoP. This is high-friction and should be reserved for major incidents where DNS/HTTP changes cannot restore traffic.

Step 3 — Validate and monitor

• Continuously poll multiple global resolvers and probe HTTP endpoints from multiple regions.
• Watch synthetic transactions and user-facing real-user monitoring (RUM) for error rates.
• Log any TTL-related cache hits that may delay recovery.

Step 4 — Communicate externally

Publish status updates every 15–30 minutes until resolved. Use the external status template below.

Step 5 — Stabilize and harden

• Once traffic is stable, raise TTLs back to standard values gradually (e.g., 300s → 1800s → 86400s) to avoid flip-flop during restoration.
• Re-enable DNSSEC and re-add DS records if you removed them. Validate signature chain.
• Rotate any emergency API keys and audit access used during the incident.

Communication templates

Internal incident start (paste into incident channel)

INCIDENT: CDN/DNS OUTAGE — [IC: @name] — Start: 2026-01-17T12:34Z
Severity: P1
Affected: www.example.com, api.example.com
Initial hypothesis: CDN edge errors (502/524) across multiple regions; DNS currently resolving
Action: DNS Lead to verify authoritative NS and lower TTL for affected records
Next update: in 15 minutes

External status page template

Title: Service disruption impacting example.com
Start: 2026-01-17T12:34Z
Impact: Some users may see errors loading www.example.com and API timeouts
What we are doing: Our DNS and networking teams are executing a pre-tested failover plan to redirect traffic to a backup CDN and origin while we work with our CDN provider
Next update: in 30 minutes

Support escalation to registrar/CDN (email)

Subject: URGENT — Active outage for example.com — Requesting emergency support
Body:
We are experiencing a major outage affecting example.com. Immediate assistance required.
Domain: example.com
Registrar account ID: 12345
Current NS: ns1.fail.example
Requested action: Change delegation to ns1-backup.example-dns.com, ns2-backup.example-dns.com
Point of contact: +1-555-0202, ops@example.com
Ticket urgency: P1

Rollback and restoration checklist

1. Confirm primary provider is stable for 48–72 hours and that the root cause is resolved.
2. Notify all stakeholders of planned rollback window and expected impact (DNS cache delays).
3. If you changed nameservers, change them back at the registrar. Ensure zone contents match and DNSSEC is re-applied in correct order (sign zone, then publish DS at registrar).
4. Gradually increase TTL: 60s → 300s → 3600s over a staging timeline to avoid rapid flips.
5. Rotate keys and audit the incident runbook actions for security and compliance.

Post-incident postmortem — structure & metrics

Run a blameless postmortem within 72 hours. Use this structure:

1. Timeline of events with timestamps and actor names.
2. Root cause analysis — what failed (DNS vs CDN vs BGP) and why.
3. Mitigations executed and their effectiveness.
4. Metrics: downtime (minutes), affected users, error rates, time-to-detect, time-to-mitigate, TTL-propagation impact.
5. Action items with owners and deadlines (e.g., add secondary DNS, test registrar API failover, add automated health checks).

Automation & testing playbook

Manual interventions are slow and error-prone. Invest in automation:

• IaC for DNS: maintain zone configurations in Terraform/CloudFormation and apply emergency-runbooks that can create or update records deterministically. See patterns for serverless data mesh that supports multi-region orchestration.
• Emergency scripts: small, auditable scripts for nameserver swaps, TTL changes and record swaps with proper logging. Keep these in a secure repo and test weekly.
• Synthetic checks: multi-region DNS and HTTP probes that can detect CDN edge failures vs DNS resolution issues.
• Chaos engineering: limited, controlled DNS failover drills to exercise the runbook and train the team. Tie these into your broader SRE practices.

Advanced strategies (2026 and beyond)

Looking forward, the following strategies are shaping resilient DNS/CDN operations in 2026:

• Multi-DNS with automated arbitration — Using multiple authoritative providers with an orchestration layer that can atomically flip delegation or reconcile zones. See pocket-edge host patterns for small-scale reliability and orchestration ideas.
• Multi-CDN with DNS steering & telemetry — Real-time steering based on performance/health signals and programmable traffic policies at the DNS level; observability patterns from edge-assisted live collaboration apply well here.
• Programmable edge and policy-driven failover — Edge compute lets teams implement HTTP-level failovers independent of CDN provider features.
• AI-assisted incident triage — Some platforms now surface likely root causes from telemetry and suggest best mitigations (evaluate AI suggestions but always verify).

Operational resilience is built before the outage. The fewer surprises your DNS and registrar interfaces present, the faster you recover.

Common pitfalls and how to avoid them

• Assuming TTLs are honored — Large resolvers sometimes cache beyond TTL; plan for a window of stuck caches.
• Forgetting DNSSEC — Removing DS records so a new provider can serve signed zones is a sensitive step; document it and automate safe rollback.
• Relying on support queues — Public support hotlines get overwhelmed during massive outages. Use registrar/CDN account managers and emergency contacts, and prefer API-driven changes where possible.
• Changing too many things — During an incident, minimize changes. Apply the smallest change that will restore service and validate it before additional changes.

Example incident timeline (concise)

Sample condensed timeline for a DNS-driven recovery:

1. T+0:00 — Detection: monitoring triggers, error spike identified.
2. T+0:05 — Declare incident, IC assigned, DNS Lead verifies NS chain.
3. T+0:12 — Secondary DNS validated; nameserver change requested via registrar API.
4. T+0:20 — Delegation change accepted; begin propagation monitoring.
5. T+0:35 — Traffic starts returning to backup records; synthetic checks green in multiple regions.
6. T+2:00 — Stabilize: increase TTL to 300s, re-enable DNSSEC (if paused) and begin postmortem capture.

Final actionable takeaways

• Inventory & script everything — If you don’t have quick, tested paths to change nameservers and records via API, you are at risk. Start from a tested incident template.
• Pre-stage backups — Secondary DNS, alternate CDN entries, and origin IPs should be pre-authorized and tested.
• Practice — Runtable drills reduce human error under pressure.
• Communicate early and often — Stakeholder trust depends on timely, accurate updates.

Call to action

Download our incident runbook checklist and pre-written automation snippets to harden your domain posture this quarter. Run your first DNS failover drill within 30 days and share the results with your SRE and product teams. If you want a template bundle (Terraform zone examples, registrar API snippets, and comms templates), request access and we’ll send the pack tailored for multi-provider setups.

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