• A cache subscriber exclusively uses the iControl system for data management, unlike other subscribers which may use either FTP or webdav for data management.  The username/password specified for the cache subscriber must be a valid iControl account on the EDGE-FX Cache system.  See the EDGE-FX Cache documentation for details on configuring such accounts.
  
  
• Cache subscribers are handled only after all other subscribers have had their content delivered and activated.  This is because the EDGE-FX Cache is presumed to be configured to get needed data from an origin server that is represented by one or more of the non-cache subscribers to a publication.  This allows a single publication to deliver updates to origin servers, and update caches with fresh content, in a single delivery cycle.
  
  
• A cache subscriber does not specify a file system directory as a destination for file delivery.  Instead, a URL base is specified for each section.  This URL base specifies the scheme, domain, and a directory path.  Each file being updated in the section is appended to this prefix to form a complete URL for presentation to the cache.  This, in turn, presumes a one to one mapping between files in the section and the URL to which the origin server will respond for that data.
  
  
• A cache subscriber supports two mutually exclusive modes, Expire and Populate, for managing cached content.
  
  The Expire mode is the closest approximation to typical cache behavior.  In the Expire mode a new or changed file causes the GLOBAL-SITE Controller to send an iControl command to purge the synthesized URL (as explained previously) from the EDGE-FX Cache.  This, in turn, forces the next access attempt by a cache client to get the URL from the origin server, even though freshness heuristics may have otherwise determined that previously-cached content could be served.  This ensures that the cache never serves stale content.
  
  The Populate mode takes the idea further by instructing the EDGE-FX Cache not only to expire any cached copy immediately, but also to immediately get a new copy from the origin server.  This allows the GLOBAL-SITE Controller to effectively prepopulate new content into an EDGE-FX Cache so that fresh, cached, content is served from the EDGE-FX Cache on the very next client request, without the need to proxy that initial request back to the origin server.  Combine this with the GLOBAL-SITE Controller's scheduled content delivery capabilities, and you can update a large set of EDGE-FX Caches with new content overnight, or whenever network load is light, to minimize surges in demand on origin servers when newly updated content is accessed on a daily cycle.
  
  

• http:// - The Expire mode purges any new, changed, or removed file from the EDGE-FX Cache.  A failure of the purge command to the EDGE-FX Cache is considered a delivery failure by the GLOBAL-SITE Controller.  The reason is that until the purge command is known to succeed, an EDGE-FX Cache could be retaining stale data.  The GLOBAL-SITE Controller reissues the same purge command until it succeeds, depending on how its normal error handling options have been configured for the publication.
  
  The Populate mode causes an immediate GET for the specified URL.  A failure to actually retrieve the URL (a 404 error) is not considered a publication failure, because in that event, the EDGE-FX Cache does not serve up stale content either.  Such an error probably represents an overall configuration failure, because it means that the EDGE-FX Cache was instructed to get data not available from the origin servers.  Such a scenario is very unlikely if the GLOBAL-SITE Controller is managing the content on multiple origin servers behind a BIG-IP Controller and a 3-DNS Controller, but not all sites are so well architected.
  
  
• mms:// - This is the scheme used for Windows media files.  The Expire mode simply purges data from the media cache, without pre-positioning.
  
  The Populate mode actually pre-positions the data to the EDGE-FX Cache.  The data is delivered directly via iControl without getting it from the origin server.  This avoids the need for the EDGE-FX Cache to ever get (potentially) large media files from the origin server at all.  The GLOBAL-SITE Controller retrieves the data once from the origin server, and then directly delivers it to the specified set of caches.  You can configure multiple GLOBAL-SITE Controllers, as you would with any subscriber, in a primary-distributor relationship to scale up delivery capability to large numbers of subscribers.
  
  ftp:// - The Expire mode behaves the same as the others, simply purging any cached data when new, changed, or removed files are delivered.
  
  The Populate mode gets the file from the specified (ftp://server.com/directory) using anonymous access only.  If anonymous access is not configured for the FTP server, this process fails.  The GLOBAL-SITE Controller treats such failures as a delivery failure, and retries delivery in subsequent delivery attempts.
  
  Only EDGE-FX Caches that are configured in forward mode have the ability to either expire or populate ftp:// requests.  If you attempt to use this scheme for caches in reverse mode, the process results in delivery failures.
  
  

Cache subscribers in non-archived publications start only with http:// or ftp://, and will not support mms:// push subscribers.

For cache subscribers to successfully use ftp:// to populate and expire files, the FTP server must be running anonymous accounts.