Trade-offs: When NOT to Use Presigned URLs

When Public CDN Is Better
For truly public content like marketing images, documentation, and product photos, presigned URLs add complexity without benefit. A public CDN provides simpler architecture with no URL generation service needed, better caching since URLs do not expire and change, lower latency with no generation round trip, and lower cost with no generation compute. Presigned URLs are access control. If you do not need access control, you do not need presigned URLs. The break even: if more than 90% of requests are for public content, consider separating to a public bucket behind CDN.
When Proxy Is Better
Presigned URLs expose storage structure in the URL including bucket names, key patterns, and provider. For sensitive applications, a proxy hides this. Proxies also enable content transformation on the fly like resize and watermark, byte range limiting to prevent full video downloads, request rate limiting per user at content level, and real time access revocation since presigned URLs cannot be revoked once issued. The tradeoff is bandwidth cost. Proxy routes all bytes through your infrastructure. For 10TB/day downloads, proxy adds 50-100% to egress costs.
🎯 When To Use: Proxy for high security, content transformation, or real time revocation needs. Presigned URLs for high bandwidth, cost sensitive workloads with adequate security.
When Signed Cookies Are Better
Signed cookies authorize access to multiple objects via single authentication. For video streaming where player requests many segments, with presigned URLs each segment needs a URL. With signed cookies, one cookie authorizes all segments in a path. Cookie approach reduces URL generation load from thousands to one, reduces client complexity with no URL management needed, and reduces request latency with no URL fetch before each segment. Limitation: signed cookies require CDN support and work at path level not individual object level.
Hybrid Approaches
Production systems often combine approaches. Common pattern: public content through CDN with no access control, private downloads via presigned URLs for bandwidth offload, sensitive uploads through proxy for validation and transformation. Decision framework: public content uses CDN, private high bandwidth uses presigned URLs, content requiring transformation or revocation uses proxy, streaming uses signed cookies where supported.

💡 Key Takeaways

✓Public content is better served through CDN - simpler architecture, better caching, no URL expiration to manage

✓Proxy is better for: hidden storage structure, content transformation, byte range limiting, or real time revocation

✓Signed cookies authorize multiple objects at path level - better for streaming with many segment requests vs thousands of URLs

✓Hybrid approach: CDN for public, presigned URLs for private high bandwidth, proxy for transformation or revocation needs

📌 Interview Tips

1When asked about access control options, present the decision framework for CDN vs presigned URLs vs proxy

2Describe a hybrid architecture where different content types use different access mechanisms based on requirements

3Explain when signed cookies are preferable to presigned URLs, particularly for streaming with many segments

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