Start with the response contract
A cache key identifies which stored response can satisfy a request. Before choosing headers, cookies and query parameters, decide which of those values actually change the content. Including every available value can fragment reuse unnecessarily. Excluding a value that changes the response can serve the wrong representation. The right policy follows the application’s behavior rather than a universal maximum-caching rule.
Separate request forwarding from variation
A service may need a request value at origin without requiring every value to create a distinct cached object. CloudFront separates relevant policy concepts, so read their responsibilities carefully. Do not assume that forwarding a header automatically means it is included in the cache key, or that a high cache-hit ratio proves the returned responses are correct.
Use a practical static-site example
Suppose /assets/logo.a1.svg is identical for all visitors. Varying its key by every analytics query parameter or unrelated cookie creates multiple entries for the same bytes. Conversely, an endpoint that produces different output for a language query requires a deliberate variation strategy. Classify paths and behaviors so a broad asset policy does not accidentally cover personalized application responses.
Choose expiration boundaries deliberately
The policy’s minimum, default and maximum TTL settings interact with response caching headers. Review the actual configured values and documented behavior instead of assuming the origin always has the final word. Use a short-lived or revalidated document policy when releases need to update HTML promptly, while versioned assets can usually support more reuse under an appropriate policy.
Account for compression variants
Compressed response handling is part of cache configuration, not simply a checkbox promising faster pages. Ensure the supported content-encoding behavior matches the origin and delivery service setup. Check that clients receive a representation they can decode and that uncompressed requests still work. Inspect response headers and transferred bytes rather than inferring effectiveness from a configured feature name.
Test correctness before tuning hit rate
Prepare requests that should share a representation and requests that should differ. Compare their response content, cache indicators and origin behavior. Repeat the exercise after changing a policy, then check release propagation. A useful cache policy reduces unnecessary origin work while preserving the distinctions the application needs; hit rate alone cannot reveal a privacy mistake or a stale document served efficiently.
Further reading
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