If your SaaS product has users in North America, Europe, and Asia, and your servers are in us-east-1, your European users are experiencing 120ms of latency before your server even starts processing their request. Your Asian users are dealing with 200ms or more. That latency compounds with every API call, every image load, and every page navigation. A CDN (Content Delivery Network) solves this by serving content from edge locations close to your users.
What a CDN actually does
A CDN caches your static assets (JavaScript, CSS, images, fonts) at edge locations around the world. When a user in London requests your application, the CDN serves static assets from a London edge node instead of your Virginia server. This reduces latency for static assets from 120ms to 5-10ms.
Modern CDNs do more than serve static files. CloudFront, Cloudflare, and Fastly can also cache API responses, run serverless functions at the edge, handle SSL termination, and provide DDoS protection. The CDN becomes your application is front door, handling traffic management before requests reach your origin servers.
Choosing a CDN
Cloudflare is the easiest to set up and offers a generous free tier. You point your DNS to Cloudflare and it automatically proxies and caches your traffic. The downside is less granular cache control compared to CloudFront or Fastly.
CloudFront integrates tightly with AWS. If your infrastructure is on AWS, CloudFront is the natural choice. It supports cache behaviors based on path patterns, custom origin configurations, and Lambda@Edge for request/response manipulation. The learning curve is steeper but the flexibility is worth it for complex applications.
Fastly offers the best cache invalidation in the industry. If your content changes frequently and you need instant cache purges, Fastly is the answer. It is more expensive and has a smaller edge network than Cloudflare, but the developer experience and VCL configuration language are excellent.
Cache strategy for SaaS applications
Static assets (JS, CSS, images) should be cached aggressively with long TTLs and cache-busting via filename hashes. When you deploy a new version, the filename changes and the CDN fetches the new file. Old versions remain cached until they expire, which is fine because no page references them anymore.
API responses require more thought. Public, non-personalized data (product catalogs, pricing pages, documentation) can be cached at the CDN with short TTLs (60 seconds to 5 minutes). Personalized data (dashboards, user profiles, account settings) should not be cached at the CDN at all. Use the Cache-Control header to control this: Cache-Control: public, max-age=300 for cacheable content and Cache-Control: private, no-store for personalized content.
SSL and security at the edge
Terminate SSL at the CDN edge, not at your origin server. This reduces the latency of the TLS handshake by performing it at a location close to the user. Configure your CDN to communicate with your origin over HTTPS as well, so the full path is encrypted.
Use the CDN is WAF (Web Application Firewall) capabilities to block common attack patterns before they reach your origin. Rate limiting at the edge is also more effective than rate limiting at your application layer because it stops abusive traffic before it consumes your server resources.
Measuring the impact
Before and after setting up a CDN, measure your Core Web Vitals from multiple geographic locations. Use tools like WebPageTest or Pingdom to test from different regions. You should see significant improvements in Largest Contentful Paint (LCP) and Time to First Byte (TTFB) for users outside your origin region. Track these metrics over time to ensure your cache hit ratio stays high and your CDN configuration remains optimal.
Need help with infrastructure performance?
traztech helps SaaS startups set up CDNs, optimize global performance, and build infrastructure that scales across regions.
Book a free strategy call