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OS X Server Essentials: Caching Content from Apple

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The Caching service speeds up the download and distribution of software and other content distributed by Apple. In this chapter from Apple Pro Training Series: OS X Server Essentials 10.9: Using and Supporting OS X Server on Mavericks, learn about the Caching service, Caching service clients, the differences between the Caching service and the Software Update service, and troubleshooting the Caching service.
From the book

Goals

  • Understand the Caching service
  • Configure and maintain the Caching service
  • Understand Caching service clients
  • Compare and contrast the Caching service and the Software Update service
  • Troubleshoot the Caching service

The Caching service speeds up the download and distribution of software and other content distributed by Apple. It caches the first download of various items distributed by Apple, then makes these items available to devices and computers on your local network. This means you can offer fast downloads of items distributed by Apple to clients on your network.

This allows you to save time as well as Internet use.

More Info ▶ ​One big new feature in the Caching service for OS X Server for Mavericks is that it serves iOS 7 devices. Apple gave this service a new name: Caching Server 2.

Reference 16.1 Understanding the Caching Service

For eligible computers and devices, the Caching service transparently caches many items, including:

  • Software updates
  • App Store purchases and downloads
  • Mac App Store purchases and downloads
  • iBooks Store purchases and downloads
  • iTunes U items
  • Internet Recovery

The Caching service supports Macs with OS X 10.8.2 or later and iOS 7 or later. It also supports iTunes content for Macs and Windows computers with iTunes 11.0.2 or later.

The network requirements to use the Caching service include the requirements to:

  • Be on a network with a network device that performs Network Address Translation (NAT) to and from the Internet
  • Have the same public IPv4 source address on the Internet side of the NAT device as on the Caching server for outgoing traffic (in simpler terms, have the same public IP address as the server behind NAT)

In order to use the Caching service with the Mac App Store, a Mac must:

  • Have OS X version 10.8.2 or later
  • Not be configured to use the OS X Server Software Update service

The key is that your clients and the Caching server(s) must share the same Internet connection behind a NAT device, and their traffic from your network to the Internet must have the same source IPv4 address. (This applies even if the client and the Caching server are on different subnets, as long as they have the same public IPv4 source address.) Fortunately, this is a common configuration.

Eligible clients will automatically use the appropriate Caching server. Otherwise, the client will use servers operated by Apple or a content distribution network partner (just like they did before the Caching service was introduced as a feature).

In the following figure, a network device performs NAT, and the organization has two subnets. The clients and the Caching servers in both subnets have the same public IPv4 source address on the public Internet side of the NAT device, even though they are in different subnets. The clients in both subnets automatically use one of the Caching servers in their organization’s network (in the figure, one subnet has two servers to illustrate that you don’t need a Caching service for each subnet behind NAT). Once the clients leave the local network, they automatically use servers controlled by Apple.

The Caching server automatically registers its public IPv4 address and local network information with Apple servers. When a client communicates with Apple servers to download an item, if the client’s public IPv4 address matches your Caching server’s public IPv4 address, the Apple servers instruct the client to get the content from the local Caching server. If the client cannot communicate with its local Caching server, it automatically downloads the content from servers controlled by Apple on the Internet.

The Caching service caches only items distributed by servers that are under Apple’s control (including items from a content distribution network partner); it does not cache content from random third parties.

Be sure to read the “Provide a Caching server” topic in the Help Center for the Server app, as it is an informative and up-to-date reference. Click the link on the Caching server pane; or in the Server app, from the Help menu, enter Provide a Caching server in the search field.

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