Incident Postmortem Template for Cross-Provider CDN/Cloud Failures

Hook: When a multi-provider CDN or DNS failure hits, you need a repeatable, precise postmortem now

Cross-provider CDN and DNS outages are noisy, complex, and expensive. As a DevOps lead or platform engineer you face fragmented telemetry, competing vendor SLAs, and overlapping caches and edge rules. The first 48 hours after an outage determine customer trust, billing exposure, and how quickly you can close the loop with engineering and legal teams. This postmortem template is built for those high-stakes, multi-provider failures and focuses on DNS, CDN, provider communication, mitigation timelines, and automating follow-up work.

Executive summary and inverted pyramid

Start with the most important facts an executive needs: impact, customer-facing status, and the top two actions taken. Keep it short and actionable. Below is the one-paragraph summary you should put at the top of every postmortem.

One-line summary: On 2026-01-16 09:38 UTC a multi-provider CDN and DNS disruption caused elevated errors for 37 percent of requests for our public API and web platform for 72 minutes. Immediate mitigation included switching to backup origins and re-routing DNS via secondary providers. Root cause: mis-synced CDN config propagation combined with expired glue records on a registrar transfer; mitigations and automated checks implemented to prevent recurrence.

Why this template matters in 2026

In late 2025 and into 2026 the industry saw two trends that changed incident response. First, organizations embraced multi-CDN and multi-region DNS as an anti-fragility strategy. Second, vendors began shipping machine-readable incident APIs and more precise edge telemetry. That combination improves resilience but increases investigation complexity. This template organizes evidence and responsibilities so you can iterate quickly and automate the low-value parts of postmortem work.

How to use this template

Copy the sections below into your incident repository or postmortem tool. Populate fields chronologically during the incident and enrich them within 48 hours. Use the checklist for DNS and CDN investigations to save time, and wire the action items into your automation pipeline so follow-ups become tests and runbook tasks.

Postmortem template for cross-provider CDN and DNS failures

1. Incident metadata

• Incident ID:
• Start: ISO 8601 UTC timestamp
• End: ISO 8601 UTC timestamp
• Detected by: monitoring tool or on-call name
• Severity: S1 / S2 etc
• Services affected: list of services, API endpoints, and regions
• Tags: CDN, DNS, provider-name, multi-cdn, multi-dns

2. Impact summary

Quantify business and technical impact succinctly. Use numbers where possible.

• Requests impacted: e.g. 37 percent of edge requests across EU/US regions
• Error taxonomy: 502 from origin, DNS NXDOMAIN, TLS handshakes failed
• Customer impact: raw numbers of paid customers affected, outages in regions, SLA exposures
• Duration: total minutes of high error rate

3. Summary timeline (high level)

Provide a tightly edited chronology of the major turning points. Use ISO timestamps and role attribution. This is what stakeholders will read first.

2026-01-16T09:38:12Z - Alert: spike in 5xx rate from edge monitoring - PagerDuty triggered
2026-01-16T09:40:05Z - On-call confirmed elevated errors and started triage
2026-01-16T09:46:30Z - Investigation: CDN A edge health shows origin failures, CDN B shows DNS NXDOMAIN for subdomain
2026-01-16T09:55:00Z - Mitigation: switched traffic to backup origin via CDN control plane
2026-01-16T10:18:00Z - Mitigation: updated DNS records with secondary provider TTLs and re-registered missing glue record
2026-01-16T11:50:00Z - Degraded metrics returned to baseline
2026-01-16T12:15:00Z - Incident declared resolved
  

4. Evidence and data sources

List the telemetry used for RCA. Attach links or references to logs, packet captures, CDN edge traces, DNS query logs, and provider incident IDs. In 2026 many providers expose incident APIs; record the provider incident IDs to correlate with vendor timelines.

• Edge request logs (sample spans)
• DNS query logs for authoritative and resolver tiers
• CDN control plane audit logs
• Registrar transfer logs and glue record history
• Provider status API events and incident IDs
• Customer support tickets and social monitoring snapshots

5. Root cause analysis

Break root cause into a primary cause and contributing factors. Be explicit about the chain of events that led to impact.

• Primary cause: e.g. CDN configuration was deployed that changed cache key behavior, causing a sudden increase in origin load while an in-progress registrar transfer removed glue records for a critical subdomain
• Contributing factors:
  • Missing automated validation for CDN config drift between providers
  • High TTLs for DNS records preventing rapid failover
  • Insufficient end-to-end SLOs around DNS resolution and edge availability

6. DNS investigation checklist

DNS is often the hidden failure mode in multi-provider outages. Follow this checklist during triage.

1. Check authoritative responses from each provider using dig at multiple public resolvers
2. Verify SOA records and serial increments to identify propagation gaps
3. Confirm glue records at registrar if delegation changed recently
4. Validate DNSSEC signatures if in use; expired signatures can cause hard failures at resolvers
5. Inspect TTLs and evaluate whether TTLs prevented failover within acceptable windows
6. Check resolver errors such as SERVFAIL or NXDOMAIN across geographic probes
7. Correlate with BGP and routing checks if names point to IP ranges that could be blackholed

7. CDN investigation checklist

CDN layers can mask root causes and make mitigation tricky. Use this checklist to rapidly map cause to effect.

1. Confirm control plane logs for the configuration change and its deployment window
2. Compare cache key and header normalization between providers in multi-CDN setups
3. Verify origin health checks and failover rules; check if the origin pool was incorrectly drained
4. Inspect signed token or TLS certificate expirations at the edge
5. Use provider edge logs to identify regional differences in error rates
6. Trigger targeted purge and test before global purge when possible

8. Provider communication and escalation log

Multi-provider outages require coordinated vendor communication. Record the full log: support ticket IDs, severity agreed with provider, public status updates, and expected resolution timelines. If a provider exposes an incident API, include the machine-readable event ID.

• Provider A ticket: ID and UTC timestamps for creation and major updates
• Provider B status API: incident ID and link to machine-readable feed
• Legal or contractual notices: record any SLA breach notices you issued or received
• Customer comms: copies of status page posts, social posts, and CS scripts

9. Mitigation timeline and decisions

This is the tactical log of decisions and mitigations. Every action should include who executed it and why the team chose that path.

Timestamp - Actor - Action - Rationale - Result
2026-01-16T09:55:00Z - On-call - Switched 20 percent traffic to backup origin via CDN B - reduce origin load - 5xx rate decreased by 12 percent
2026-01-16T10:18:00Z - DNS Engineer - Re-added glue record at registrar - delegated names resolved globally - NXDOMAIN resolved within 8 minutes
2026-01-16T10:40:00Z - Platform Lead - Deployed CDN config rollback to previous stable revision - prevent further cache-key divergence - errors dropped to baseline
  

10. Action items and owners

Convert the postmortem into concrete, tracked work. Prefer small, testable tasks that can be automated and verified.

• Short term (within 7 days):
  • Automate glue record validation as part of registrar workflows - owner: DNS team
  • Add pre-deploy CDN config diff checks to CI - owner: platform infra
• Medium term (30 days):
  • Implement synthetic multi-region DNS resolution checks and alerting - owner: SRE
  • Add automated provider incident ingestion to our Slack channel via status APIs - owner: observability
• Long term (90 days):
  • Adopt policy-driven IaC gates for CDN changes with canary rollout automation - owner: platform
  • Run quarterly chaos sessions targeting DNS and CDN failover scenarios - owner: reliability engineering

11. Follow-up automation and runbook integration

The most impactful part of the postmortem is turning findings into automation so the same incident never repeats. Below are concrete automations to implement and verify.

• Automated postmortem starter: When an incident is resolved, trigger a postmortem template population from incident events using your incident API and telemetry. This reduces cognitive load and capture drift.
• Registrar and glue record CI checks: Add a CI job that verifies delegation and glue entries before approving DNS-related PRs. Failing the check blocks merge.
• Multi-CDN config diff and policy checks: Use a linter that validates cache keys, header normalization, and origin pool definitions across providers. See guidance on multi-CDN publishing.
• Automated SLO impact calculation: On incident close, compute SLO burn and attach it to postmortem automatically. Consider billing signals and query-cost effects documented for cloud teams.
• Runbook task automation: Convert mitigation steps into executable runbook steps with scripts for traffic shift, purge, and DNS update that can be invoked from the incident console. Use safe automation patterns from your agent and automation playbooks.

12. Runbook snippet examples

Store these snippets in your runbook repository. They serve as building blocks for on-call actions and automation.

# DNS delegation check pseudo-YAML
check-delegation:
  - query: dig +short ns example-subdomain.company
  - query: dig +short soa company
  - evaluate: if delegation mismatch then fail

# CDN traffic shift pseudo-YAML
shift-traffic:
  - api-call: set-cdn-weight cdnA origin-primary 0.2
  - api-call: set-cdn-weight cdnB origin-backup 0.8
  - validate: monitor error-rate until stable
  
# Post-incident automation starter pseudo-YAML
on-incident-resolve:
  - extract: incident-metadata
  - create: postmortem-document prefilled
  - assign: action items to owners
  - schedule: automation tasks in CI pipeline
  

13. Public summary and customer communication

Your public post should be short, non-technical, and transparent. Include timeline, impact, and remediation. Link to the full technical postmortem internally if appropriate. Keep legal and PR teams in the loop before public posting.

Example public blurb: We experienced a service disruption on 2026-01-16 that affected some customers for up to 72 minutes. The issue was resolved and we have implemented measures to reduce the chance of recurrence. More details will be provided in a technical postmortem.

14. Lessons learned and prevention

Capture meta-issues that contributed to the incident so teams can prioritize organizational changes.

• Need for standardized incident ingestion across providers to speed correlation
• Insufficient automation around registrar and DNS delegation changes
• Overreliance on manual CDN config syncs between providers

15. Verification and closure

Closure requires verification. Include acceptance criteria and tests that prove action items were implemented and effective.

• All action items have owners and target dates
• Synthetic DNS and CDN checks added to observability and passing for 14 days
• CI gates for CDN and DNS changes are enabled and blocking bad merges
• Quarterly chaos test scheduled and added to team calendars

Operational playbook: quick decision matrix

Use this when deciding whether to rollback, shift traffic, or change DNS delegation during an incident.

• If errors are localized to one CDN region and origin health is stable: prefer traffic shift to healthy edges
• If DNS shows delegation issues: do not change edge configs first; fix delegation at registrar and validate global resolution
• If TLS or cert issues are present at edge: rotate certs on edge provider and shift traffic while new cert propagates
• If multiple providers are impacted simultaneously: escalate to coordinated provider support and consider global traffic diversion to unaffected backends

2026 advanced strategies and future predictions

Expect these trends to shape incident practices this year and beyond.

• Machine-readable incident feeds: More providers will support incident APIs, enabling automated correlation and faster joint RCA. See examples of machine-readable incident APIs.
• Policy-as-code for edge: Teams will encode safety checks in CI to prevent misconfigurations across CDNs. Consider guidance around policy-driven approaches.
• DNS observability at the edge: Edge probes combined with DoH and DoT telemetry will make DNS failures easier to detect and quantify.
• Runbooks as executable playbooks: Runbooks will be tightly integrated with automation platforms, letting on-call enact rollback with reproducible scripts. Look to emerging automation agent patterns for safe execution.
• Regular multi-provider chaos testing: Organizations adopting multi-CDN will include cross-provider failover tests as standard practice.

Actionable takeaways

• Adopt this postmortem template and populate it during incidents to reduce rework.
• Automate registrar and glue record checks as part of DNS change workflows.
• Implement multi-CDN config diffs and CI gates to prevent propagation of divergent rules.
• Wire provider incident APIs into your incident console for faster vendor correlation. See patterns for incident ingestion.
• Convert mitigation steps into executable runbook tasks and test them with chaos exercises.

Closing: Keep the loop short, automate the follow-up

Multi-provider CDN and DNS failures expose gaps in tooling, process, and automation. Use this template to focus your postmortem work on what matters: clear timelines, owner-driven action items, and automations that convert human decisions into repeatable, testable steps. That converts painful lessons into lower risk.

If you want a ready-to-use repository, copy the template into your incident management system and schedule an automation sprint to implement the top three action items within 30 days. That single investment typically halves time-to-recover on repeat incidents.

Call to action

Use this template in your next incident and automate at least one post-incident task this quarter. Share your results with the team and iterate. For platform teams building runbooks, standardize the template in your GitOps repo and add CI validation so every change becomes safer by default.

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