Dispatcher ETag Enhancement for CDN Revalidation

Overview

The INTERNAL_AEM_DISPATCHER_ETAG_ENHANCEMENT flag enables Dispatcher to evaluate the If-None-Match request header on cache hits. When the incoming If-None-Match value matches the cached ETag, Dispatcher can return 304 Not Modified instead of 200 OK.

This behavior is designed to reduce unnecessary payload transfer between CDN and Dispatcher and increase conditional-cache efficiency.

Availability

AEM as a Cloud Service support

In AEM as a Cloud Service, this capability is supported for customer use.

Customers can enable it by setting the INTERNAL_AEM_DISPATCHER_ETAG_ENHANCEMENT environment variable in Cloud Manager. Adobe can also enable it on behalf of the customer when needed.

When enabled, and when the CDN sends If-None-Match and the relevant ETag is present in Dispatcher cache, higher 304 response rates between CDN and Dispatcher are expected. This increase is the intended outcome.

Configuration example (cache ETag header)

For this enhancement to be effective, make sure Dispatcher caches the ETag response header and your web server is configured to avoid generating file-system-based ETags.

Example dispatcher.any cache section:

/cache {
  /headers {
    "Cache-Control"
    "Content-Type"
    "Expires"
    "Last-Modified"
    "ETag"
  }
}

Example Apache directive in the Dispatcher vhost context:

FileETag none

For baseline header-caching guidance, see Caching HTTP response headers.

Validation example

After enabling the environment variable and deploying config changes:

Public reference (related behavior)

For customer-facing baseline guidance on header caching and ETag handling in Dispatcher, reference:

“This capability is available in Dispatcher 2.0.264 (AEM SDK 2026.2.24464). When enabled, Dispatcher can validate If-None-Match against cached ETag values and return 304 Not Modified on cache hits. In AEM as a Cloud Service, this is supported and can be enabled through Cloud Manager environment configuration.”