Introduction to cache policies - Edge Security Acceleration

Edge Security Acceleration (ESA) improves website performance by caching static resources on a distributed network of points of presence (POPs). This reduces origin requests, lowers latency, and lets you fine-tune caching behavior to match your traffic patterns.

Caching benefits

ESA boosts your cache hit ratio with policies like ignoring or sorting query string parameters, consolidating requests for identical content into a single cache entry and eliminating redundant origin requests.
Cache policies can be adjusted dynamically — for example, bypassing the cache during debugging or canary releases.
Serving content from the cache reduces latency, improves user experience, and lowers load on your origin server.

Default rules and development mode

By default, ESA caches static resources — images, CSS, and JS files — on edge POPs, reducing origin traffic and improving response times. Development mode lets you bypass the cache entirely and route requests directly to the origin, which is useful when testing changes or running a canary release.

Enable development mode: Bypass cache components to access the origin server directly. This is useful for canary releases or debugging.

Note
Enabling this feature can significantly increase back-to-origin traffic. Disable development mode after you finish debugging.
Default cache rules: ESA automatically caches static resources, such as images and CSS/JS files, on edge POPs to prioritize user requests.

Set the cache TTL

Configure the browser and edge cache time-to-live (TTL) to balance freshness with performance. By default, TTL follows the origin server's Cache-Control header, but you can override it per resource type or path.

Browser cache TTL: Override the origin's Cache-Control header to set a custom TTL. Set static resources to 30 days, use shorter TTLs for frequently updated content, and longer TTLs for cold data.
Edge cache TTL: Set TTL by directory (such as /images/*) or file extension (such as .jpg,.css). For frequently updated resources, use 3600 seconds. For infrequently accessed resources, use 86400 seconds.

Increase the cache hit ratio

Query string handling is a common source of cache misses. Requests for the same resource with different parameter names or ordering are treated as separate cache entries by default. Two options let you consolidate these into a single cache key.

Ignore query strings: Enable the query string feature to cache requests that share the same URL path but have different ?param=value parts as a single resource. For example, example.com/index.html?v=1.0 and example.com/index.html?v=2.0 are treated as the same resource.
Sort query strings: Enable the query string sorting feature to treat requests with the same parameters in a different order as the same cache key. For example, /api?a=1&b=2 and /api?b=2&a=1 map to the same cache entry.

Advanced features

ESA provides tiered cache and cache reserve to help you optimize resource use, improve user experience, lower costs, and reduce bandwidth pressure on your origin server.

Multi-level cache: Tiered cache is an advanced performance optimization technique. ESA caches origin resources on tiered cache nodes worldwide, so data is served from the POP closest to the user, improving overall system performance and efficiency.

Cache reserve: When enabled, ESA routes origin requests for cold traffic (infrequently accessed requests) to a specified cache reserve instance. This feature is suitable for infrequently accessed resources that require long-term storage. Cache reserve POPs use dedicated disk space to hold files for the specified duration, preventing eviction due to low popularity and avoiding unnecessary egress traffic fees from the origin.