The Dispatcher is Adobe Experience Manager’s caching and/or load-balancing tool that helps realize a fast and dynamic Web authoring environment. For caching, the Dispatcher works as part of an HTTP server, such as Apache. It has the aim of storing (or “caching”) as much of the static website content as possible and accessing the website’s layout engine as infrequently as possible. In a load-balancing role, the Dispatcher distributes user requests (load) across different AEM instances (renders).
For caching, the Dispatcher module uses the Web server’s ability to serve static content. The Dispatcher places the cached documents in the document root of the Web server.
The Dispatcher uses the web server’s ability to serve static content. The Dispatcher stores cached documents in the web server’s document root. The Dispatcher has two primary methods for updating the cache content when changes are made to the website.
Load-balancing distributes user requests (load) across several AEM instances. The following list describes the advantages for load-balancing:
For further details, see the Dispatcher Overview page
You can download the latest Dispatcher module from the Dispatcher Release Notes page.
Refer to the Installing Dispatcher page
See the Configuring Dispatcher page.
See Using Dispatcher with an Author Instance for the detailed steps.
You can configure the CQ Dispatcher with multiple domains, provided the domains satisfy the following conditions:
Read Using Dispatcher with Multiple Domains for further details.
You can use the sticky connections feature, which ensures that all documents for a user are processed on the same instance of AEM. This feature is important if you use personalized pages and session data. The data is stored on the instance. Therefore, subsequent requests from the same user must return to that instance or the data is lost.
Because sticky connections restrict the Dispatcher’s ability to optimize requests, you should use this approach only when necessary. You can specify the folder that contains the “sticky” documents, thus ensuring all documents in that folder are processed on the same instance for a user.
For most pages that use sticky connections, you should turn off caching. Otherwise, the same instance of the page is displayed to all users, regardless of the session content.
For some applications, it can be possible to use both sticky connections and caching. For example, if you display a form that writes data to a session, you can use sticky connections and caching in tandem.
Yes, if the machine is sufficiently powerful. However, it is recommended that you set up the Dispatcher and the AEM Publish instance on different machines.
Usually, the Publish instance resides inside the firewall and the Dispatcher resides in the DMZ. If you decide to have both the Publish instance and Dispatcher on the same physical machine, ensure that the firewall settings prohibit direct access to the Publish instance from external networks.
Yes. For example, if you want to cache only GIF files, specify *.gif in the cache section of the dispatcher.any configuration file.
You can delete files from the cache by using an HTTP request. When the HTTP request is received, Dispatcher deletes the files from the cache. Dispatcher caches the files again only when it receives a client request for the page. Deleting cached files in this manner is appropriate for web sites that are not likely to receive simultaneous requests for the same page.
The HTTP request has the following syntax:
POST /dispatcher/invalidate.cache HTTP/1.1 CQ-Action: Activate CQ-Handle: path-pattern Content-Length: 0
Dispatcher deletes the cached files and folders that have names that match the value of the CQ-Handle header. For example, a CQ-Handle of
/content/geomtrixx-outdoors/en matches the following items:
All files (of any file extension) named en in the geometrixx-outdoors directory.
Any directory named
_jcr_content below the en directory (which, if it exists, contains cached renderings of subnodes of the page).
en is only be deleted if the
For further details on this topic, see Manually Invalidating the Dispatcher Cache.
See the Caching Secure Content page.
Question: The business has recently faced a problem at Dispatcher level. One of the AJAX calls which was getting some data form CQ repository had
jcr:content in it. That got encoded to
jcr%3acontent resulting in that wrong result set.
ResourceResolver.map() method to get a ‘Friendly’ URL to be used / issued get requests from and also to solve the caching issue with Dispatcher. The map() method encodes the
: colon to underscores and the resolve() method decodes them back to SLING JCR readable format. Use the map() method to generate the URL that is used in the Ajax call.
See the Replication page.
If Delete operations are causing the Dispatcher to flush, use the workaround in this community blog post by Sensei Martin.
You can use the “chain replication” feature. With this feature enabled, the Dispatcher flush agent sends a flush request when a replication is received from author.
To enable it:
How does the Dispatcher determine if a document is up-to-date?
To determine whether a document is up-to-date, the Dispatcher performs these actions:
It checks whether the document is subject to auto-invalidation. If not, the document is considered up-to-date.
If the document is configured for auto-invalidation, the Dispatcher checks whether it is older or newer than the last change available. If it is older, the Dispatcher requests the current version from the AEM instance and replaces the version in the cache.
You can define whether the Dispatcher caches a document by using the Dispatcher configuration file,
dispatcher.any. The Dispatcher checks the request against the list of cacheable documents. If the document is not in this list, the Dispatcher requests the document from the AEM instance.
/rules property controls which documents are cached according to the document path. Regardless of the
/rules property, Dispatcher never caches a document in the following circumstances:
The Dispatcher stores cached files on the web server as if they were part of a static website. If a user requests a cached document, the Dispatcher checks whether the document exists in the web server’s file system. If so, the Dispatcher returns the documents. If not, the Dispatcher requests the document from the AEM instance.
The GET or HEAD (for the HTTP header) methods are cacheable by the Dispatcher. For additional information on response header caching, see the Caching HTTP Response Headers section.
Yes. In such cases, ensure that both the Dispatchers can access the AEM website directly. A Dispatcher cannot handle requests coming from another Dispatcher.