CDNMigrationPerformance

Migrating a High-Traffic Site Off an Affected CDN: Step-by-Step Guide

UUnknown

2026-02-18

11 min read

A practical, API-first plan to switch CDNs with near-zero downtime: TTL strategy, TLS migration, cache warming, and rollback steps for 2026.

Hook: When your CDN goes dark — migrate fast, safely, and with confidence

If a major CDN outage in late 2025 taught the industry anything, it was this: high-traffic sites can't afford long, manual migrations when their edge provider becomes unreliable. You're here because you need a battle-tested plan to switch CDNs with minimal downtime, no SEO loss, and a fail-safe rollback.

Overview — What this guide gives you (in 2026)

This article delivers a practical, chronological migration plan for moving a high-traffic site from one CDN provider to another. It focuses on the tasks that cause the most outages and SEO damage: DNS TTL strategy, certificate migration, cache warming, monitoring and observability, and a clear rollback procedure. It includes API-driven steps, example commands, and a timeline you can run as a checklist.

Why this matters now (2026 trends)

In 2025–2026 the web edge evolved: CDNs are programmable (Workers/Edge Functions), HTTP/3 and QUIC are near-ubiquitous, and many teams rely on CDN-managed TLS and edge compute. That increases the blast radius of a CDN outage. Simultaneously, multi-CDN and API-first infrastructure became standard for resilience. This guide assumes you want a quick cutover without breaking analytics, SEO, or user experience.

High-level migration strategy (inverted pyramid)

Prepare: replicate config, provision certs, and keep the old CDN live.
Lower DNS TTL and set monitoring and health checks.
Provision the new CDN and validate configuration in a staging hostname.
Warm caches and pre-provision TLS via ACME/DNS challenges.
Cut traffic gradually using DNS or weighted routing.
Monitor, validate, and then raise TTL and finalize.
Rollback plan always ready: DNS flip or load balancer weight revert.

Pre-migration checklist (T-72 to T-24 hours)

Before any DNS change, do these items. Treat this as immutable.

Inventory: List hostnames, origin endpoints, caching rules, WAF rules, edge functions, custom headers, and origin health checks.
Export config: Download or script-export ACLs, edge rules (VCL/WAF), page rules, and redirects from the old CDN.
Keep the old CDN live: Don't purge or modify production config on the old provider until migration completes and you’ve verified the new provider.
Provision accounts: Create the new CDN account and enable any needed enterprise features (geo routing, TLS upload, advanced logging).
Confirm origin access: Ensure the new CDN POPs can reach your origin IPs (allow whitelist IPs or authenticate via tokens).
Plan certificate approach: Use ACME with DNS challenge where possible to avoid key material transfer. If you must upload keys, prepare secure transfer procedures and ensure private key protection (HSM or encrypted transfer).

TLS / Certificate migration options

Choose one of three paths based on risk, speed, and compliance.

ACME/DNS challenge (recommended) — Provision new certs on the new CDN using DNS-01 automation. This avoids exporting private keys and scales well for wildcard certs.
Upload existing cert and key — Fast if allowed by policy. Only use if you can securely export the private key and the receiving CDN accepts uploaded keys.
Provider-managed certs — Use the CDN's managed TLS (e.g., Cloudflare Universal or similar). Fast but requires DNS changes or CNAME verification depending on provider.

Example: Using acme.sh to provision a wildcard cert via DNS for example.com (replace with your DNS provider hook):

acme.sh --issue --dns dns_provider -d example.com -d '*.example.com' --key-file /tmp/site.key --fullchain-file /tmp/site.crt

DNS TTL strategy (best practices)

DNS is the most visible control for traffic cutover. Use these rules:

Lower TTL early — Reduce authoritative TTL to 60–120 seconds at T-72h to give caches time to respect the lower value. Many resolvers ignore TTLs under 60s; 60s is a practical target.
Consider negative caching — If you change CNAME/ALIAS records, remember SOA negative caching (minimum TTL) can affect behavior.
Avoid TTL = 0 — Some resolvers treat zero as maximum caching. Use 60s–120s instead.
DNSSEC & DS records — If you're using DNSSEC, plan DS updates; they can complicate cutovers. Test in staging where possible.

If your DNS provider supports weighted routing (Route53, NS1), use weighted DNS during the cutover to shift percentages of traffic to the new CDN before full switch.

Example commands: check DNS propagation

dig +short @8.8.8.8 www.example.com
# or trace the resolution path
dig +trace www.example.com

New CDN provisioning — mirror key configurations

Configure the new CDN to match production behavior. Key areas:

Caching rules & TTL — Map your origin cache-control headers to CDN TTLs (respect origin, override where necessary).
Edge logic — Translate edge functions (Cloudflare Workers, Fastly VCL, Akamai EdgeWorkers) to the platform’s language.
Headers & cookies — Ensure important headers (X-Forwarded-For, True-Client-IP, X-Cache) are preserved.
Security — Recreate WAF rules, bot management, rate limits, and DDoS configs.
Logging — Enable access logs and real-user monitoring (RUM) and direct them to your analytics and SIEM solutions; don't lose visibility during cutover. Consider data sovereignty and local storage needs when routing logs across regions.

Staging hostname validation

Create a staging hostname (staging.example.com) that uses the new CDN but points to the same origin. Validate:

Origin reachability from edge POPs
Edge logic behavior (redirects, A/B tests)
TLS handshake, certificate names, and chain
Logging and analytics forwarding

Cache warming techniques (critical for high-traffic sites)

Cold caches equal slow page loads. Use multiple, complementary methods to warm the new CDN across POPs:

Synthetic parallelized prefetch — Run parallel GET requests for key URLs distributed across POPs and regions. Use a fleet of workers or cloud functions (Lambda, Cloud Run) to exercise POPs simultaneously.
```
# simplified curl loop; run from multiple regions
for url in $(cat top_urls.txt); do
  curl -s -H "User-Agent: cache-warm" "https://www.example.com/$url" > /dev/null &
done
wait
```
CDN prefetch APIs — Many CDNs (Fastly, Akamai, Cloudflare and others) now offer prefetch or preload APIs to instruct POPs to fetch specific assets. Use those where available to avoid origin strain.
Surrogate keys & selective purges — Tag assets and use surrogate-key based prefetch/purge to target groups of files.
Use HTTP/3/QUIC where possible — Modern POPs will serve faster; ensure your client fleet tests QUIC to validate behavior.

Aim to warm the top 1–5% of your most-requested URLs first. For e-commerce, prefetch PDPs and category pages. For media, prefetch CDN manifests and key media chunks.

Cutover methods — choose what fits your stack

Pick one of these cutover methods depending on your DNS provider and traffic patterns.

DNS flip (simple, widely usable)

At T0, change the A/CNAME to point to the new CDN's target.
Monitor traffic percentage via RUM and edge headers.
If problems arise, revert DNS to the old CDN's records (remember TTL).

Weighted DNS / Traffic steering (safer for large sites)

Use a DNS provider with weighted routing (Route53, NS1) or a global load balancer.
Start with 5–10% to new CDN, increase over 30–60 minutes to 50%, then to 100% if healthy.
If issues occur, reduce weight back to the previous value instantly.

Layer-7 load balancer or reverse-proxy (fast rollback)

If you run a global load balancer that supports origin pools (e.g., Cloud Load Balancer, Akamai GSLB), add the new CDN as a pool and shift weights. This avoids DNS caching and gives near-immediate rollback.

Verification checklist during cutover

Monitor these signals in real time:

Edge headers: Check for new CDN headers (CF-Cache-Status, X-Cache) via curl -I. See tools for cache and DNS testing.
Performance: RUM metrics: LCP, TTFB, FCP by region.
Origin load: Watch origin CPU, bandwidth, and error rates to ensure prefetch didn’t overload origin.
Errors: 5xx spikes — if seen, immediately reduce traffic to the new CDN.
SEO: Verify 200/301 responses for canonical pages and robots.txt. No new 4xx/5xx for crawlers.

Rollback procedure (your fastest route to safety)

Have a documented and rehearsed rollback. The fastest options:

DNS revert: Re-point the hostname to the old CDN DNS records. Because you lowered TTL earlier, most clients will switch back within 60–120s. Keep TTL low during the window.
Weighted revert: Reduce new CDN weight to 0 in your DNS/load balancer and increase previous provider back to 100%.
Edge config toggle: If both CDNs are behind a load balancer, swap pool weights or re-enable the old pool.

Critical: do not delete the old CDN configuration until post-migration cleanup is complete. Preserve logs and edge configs for at least one week to diagnose issues and compare metrics.

Post-migration (T+24h to T+7d)

Raise the authoritative TTL back to 300–3600s after 24–48 hours of stable traffic.
Finalize WAF and bot rules. Bring any staged protections to production once confident.
Check SEO-critical pages for status codes, canonical tags, hreflang, and structured data. Use Search Console and Bing Webmaster Tools to monitor indexing changes.
Compare performance and error budgets against SLAs. If metrics are worse, review edge rules and purge/prefetch as needed. See also edge orchestration approaches for longer-term stability.
Close the loop with billing and contract changes; ensure you stop billing on the old provider if you no longer need it.

Monitoring, observability, and analytics

Use both synthetic checks and real-user monitoring. Key integrations:

RUM (e.g., New Relic Browser, Datadog RUM) for LCP/CLS/TTFB trends.
Synthetic checks from multiple regions (Uptrends, Catchpoint, ThousandEyes).
Edge logs to your logging pipeline (S3, BigQuery, ELK) for fast forensic analysis.
Alerting on 5xx rate, origin latency, error budget burn rate. Consider edge-oriented cost optimizations while you scale monitoring data.

Developer & automation tips (APIs and tooling)

Automate repeatable steps with scripts and CI/CD:

CDN APIs: Most CDNs provide REST APIs to configure services, purge caches, and provision TLS. Script exports and imports (e.g., Fastly VCL uploads, Cloudflare API zone settings).
Infrastructure as code: Use Terraform providers for CDNs where available to version and reproduce configs; treat CDNs like code and follow a versioning approach.
CI pipelines: Add a pipeline job to perform staged prefetch/purge and to validate key headers before promoting any change to production DNS. For teams building skills in automation, see guides on upskilling with AI-guided learning.
Canary tests: Run automated canaries that validate page renders, API responses, and checkout flows on the new CDN; integrate with your edge-backed workflows for reproducible validation.

Real-world example (case study summary)

In December 2025 a retail site with 150M monthly sessions moved off a single-CDN setup after an outage. They lowered TTL to 60s at T-72h, provisioned wildcard certificates via ACME with DNS-01, warmed top PDP pages via a 50-region Lambda fan-out, and used weighted DNS to shift traffic from 0% to 100% in 6 steps. Rollback was never needed; LCP improved by 12% and origin error rates dropped by 35%.

Common pitfalls and how to avoid them

Not warming cache: Leads to origin overload and slow pages. Pre-warm top pages and assets. See testing for cache-induced SEO mistakes.
SSL misconfiguration: Missing SANs or intermediate certs cause browser errors. Validate cert chains on multiple clients.
TTL too high during cutover: Forces long propagation and recovery times. Lower TTL early and keep it low until stable.
Deleting old config early: Prevents rollback. Keep the old CDN running until fully confident.
Ignoring bots and crawlers: If crawlers hit a cold cache, indexing can be slowed. Warm /robots.txt and top crawler pages.

Quick checklist (printable)

Inventory & export old config
Lower TTL to 60–120s (T-72h)
Provision new CDN, setup TLS (ACME recommended)
Validate on staging hostname
Warm cache (synthetic + prefetch APIs)
Cutover via DNS flip or weighted routing
Monitor: RUM, edge logs, origin metrics
Raise TTL after 24–48h stable
Keep old provider config for 7 days before decommission

Final thoughts — resilience is programmatic

By 2026, CDN migrations are an operational competency, not a risky migration weekend. Treat CDNs like code: automate, test, and version everything. Maintain multi-CDN readiness, use API-driven tooling for fast cutovers, and always have an explicit rollback trigger.

Actionable next steps (start now)

Run the printable checklist in a dry run on a staging domain today.
Automate TLS provisioning via ACME/DNS for your domains.
Script a cache-warm job and test it across three regions.

Call to action

Need a migration plan tailored to your stack? Our migration playbooks and automation templates for Cloudflare, Fastly, and CloudFront include Terraform modules, ACME scripts, and prebuilt cache-warm runners. Contact us for a free migration readiness review and a customized cutover script.

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