Decide what the CDN should deliver
Begin with an inventory. Separate versioned assets such as images, stylesheets, scripts, fonts, and downloads from HTML, APIs, account pages, checkout, and administration. CDNs often fill a cache on demand: the first request can reach the origin, while later matching requests may be served at the edge. A nearby edge and a cache hit are different benefits.
Record the host, application, storage bucket, or load balancer that supplies each path; it must answer a cache miss.
Start with assets identical for every visitor that can safely remain available until their stated lifetime ends.
Do not share personalized dashboards, session-bound pages, or customer data unless a qualified engineer has designed and tested separation.
Set cache policy from content behavior
HTTP response headers express cache behavior. Cache-Control says whether a response may be stored and how long it stays fresh; a time to live, or TTL, is that freshness period. A browser is a private cache, while a CDN is usually shared. Use explicit headers. The HTTP standard lets s-maxage set a shared-cache lifetime separately from max-age.
Publish a new URL when content changes, such as a content-hashed filename, then give the immutable version a long documented lifetime.
Choose a short lifetime or validation behavior based on the cost of stale content; do not reuse an asset rule for prices, inventory, or account state.
Use private for responses intended for one user. A cookie alone does not make a response safe for a shared cache.
Make invalidation an exception, not the release plan
Invalidation, or purging, tells a managed CDN to drop selected stored objects before normal expiry. Use it for corrections, not every deploy. Confirm that the origin already returns the replacement before purging; otherwise a refill can preserve the bad response. Browser caches are outside the CDN’s purge control, so URL versioning remains dependable for changing files.
Prefer a specific path, release group, or provider-supported cache tag over a whole-site purge; broad misses can suddenly load the origin.
A distributed purge may not reach every edge at once. Check the provider’s completion semantics and test a representative URL.
Record the old and new URL, cache rule, purge scope, expected result, and reversal step.
Keep the origin behind the delivery layer
Direct origin access can bypass CDN caching and edge controls. Restrict it so the CDN, and only intended paths, can reach it. Depending on your stack, use cloud-origin access control, firewall rules with documented CDN egress ranges, private networking, signed origin requests, or mutual TLS (mTLS), where both sides authenticate with certificates.
From an authorized test location, confirm the origin rejects public requests while the CDN hostname works.
Scope health checks, deployment tools, and internal access by identity and network rather than a broad public rule.
Origin authentication differs by CDN and origin. Use current provider setup guidance and security review.
Treat TLS as two connections
HTTPS at the edge protects the visitor-to-CDN connection, but the CDN-to-origin connection needs protection too. Require encryption on both legs, validate the origin certificate for the CDN mode, and assign hostname and renewal ownership. OWASP recommends TLS 1.3 by default and permits TLS 1.2 for compatibility; it says TLS 1.0 and 1.1 should be disabled. Obtain qualified review for regulated data, payment flows, or unusual client compatibility.
List the edge and origin certificate owners, renewal routes, and failure response.
Test HTTP-to-HTTPS, canonical-host, and deep-link redirects for loops or lost paths.
Encryption does not make a response safe to cache; set cache rules separately for authenticated, personal, and payment-adjacent pages.
Test the real delivery path before changing traffic
Start on a staging hostname or narrow production path, then test the CDN hostname, not only the origin. Chrome DevTools Network shows request status, domain, timing, size, and headers. Test an empty-cache hard reload to approximate a first visit, then a repeat visit to inspect reuse. Compare expected headers and content, not just a faster-looking page. Repeat from representative regions when the audience is spread out.
Inspect Cache-Control and provider cache-status headers. Confirm public assets reuse and sensitive pages are not unexpectedly shared.
Exercise a miss, stale-content correction, origin error, and rollback of one asset or route before a broad launch.
Save tested URLs, header captures, route-rule version, and before-and-after timings with the change record.
Choose a CDN by operating needs, then prove it
Do not choose a CDN solely by point-of-presence count or a generic speed claim. Performance varies with geography, time, traffic distribution, routing, and cache hit ratio. Compare candidates on representative routes, assets, and regions. Ask whether each supports your needed cache controls, targeted invalidation, origin restriction, certificate workflow, logs, access roles, pricing, support, and change process.
Use identical cache headers, origin behavior, and pages for candidates; record first-visit and repeat-visit results separately.
Review request, transfer, invalidation, logging, and support costs, plus a cache-miss surge. Pricing and controls vary by plan.
Require exportable configuration, least privilege, tested rollback, and clear ownership before covering critical routes.