AEM Publish

The AEM Publish service has two primary caching layers, the AEM as a Cloud Service CDN and AEM Dispatcher. Optionally a customer managed CDN can be placed in front of the AEM as a Cloud Service CDN. The AEM as a Cloud Service CDN provides edge delivery of content, ensuring experiences are delivered with low latency to users around the world. AEM Dispatcher provides caching directly in front of AEM Publish, and is used to mitigate unnecessary load on AEM Publish itself.

CDN

AEM as a Cloud Service’s CDN’s caching is controlled by HTTP response cache headers, and is intended to cache content to optimize a balance between freshness and performance. The CDN sits between the end-user and the AEM Dispatcher, and is used to cache content as close to the end user as possible, ensuring a performant experience.

Configuring how the CDN caches content is limited to setting cache headers on HTTP responses. These cache headers are typically set in AEM Dispatcher vhost configurations using mod_headers, but can also be set in custom Java™ code running in AEM Publish itself.

When are HTTP requests/responses cached?

AEM as a Cloud Service CDN caches only HTTP responses, and all the following criteria must be met:

By default, HTTP responses not cached by AEM Dispatcher automatically have any HTTP response cache headers removed to avoid caching at CDN. This behavior can be carefully overridden using mod_headers with the Header always set ... directive when necessary.

What is cached?

AEM as a Cloud Service CDN caches the following:

Typically an HTTP request/response for a single URL is cached as a single object. However, the CDN can handle caching multiple objects for a single URL, when the Vary header is set on the HTTP response. Avoid specifying Vary on headers whose values do not have a tightly controlled set of values, as this can result in many cache misses, reducing cache hit ratio. To support caching of varying requests at AEM Dispatcher, review the variant caching documentation.

Cache life cdn-cache-life

The AEM Publish CDN is TTL (time-to-live) based, meaning that the cache life is determined by the Cache-Control, Surrogate-Control, or Expires HTTP response headers. If the HTTP response caching headers are not set by the project, and the eligibility criteria are met, Adobe sets a default cache life is 10 minutes (600 seconds).

Here is how the cache headers influence the CDN cache life:

Use Cache-Control to control the cache life when it is the same for both browser and CDN. Use Surrogate-Control when the web browser should cache the response for a different duration than the CDN.

Default cache life

If an HTTP response qualifies for AEM Dispatcher caching per above qualifiers, the following are the default values unless custom configuration are present.

How to customize cache rules

Configuring how the CDN caches content is limited to setting cache headers on HTTP responses. These cache headers are typically set in AEM Dispatcher vhost configurations using mod_headers, but can also be set in custom Java™ code running in AEM Publish itself.

AEM Dispatcher

When are HTTP requests/responses cached?

HTTP responses for corresponding HTTP requests are cached when all the following criteria are met:

What is cached?

AEM Dispatcher caches the following:

Cache life

AEM Dispatcher caches HTTP responses using the following approaches:

Default cache life

If an HTTP response qualifies for AEM Dispatcher caching per above qualifiers, the following are the default values unless custom configuration are present.

How to customize cache rules

The AEM Dispatcher’s cache can be configured via the Dispatcher configuration including:

Using mod_headers to set cache headers the vhost configuration will not affect Dispatcher caching (TTL-based) as these are added to the HTTP response after AEM Dispatcher processes the response. To affect Dispatcher caching via HTTP response headers, custom Java™ code running in AEM Publish that sets the appropriate HTTP response headers is required.