| Tiered Electronic Distribution in ZENworks for Servers 3 comprises the following components: Distributor. This is a Java software process that runs on a NetWare server and as a service on a Windows NT/2000 Server. This software is responsible for distributing the files to the subscribers in the network. The distributor also calls on some TED agents to collect the files and bundles them into a distribution that can then be sent to the subscribers (see the next item). Subscriber. This is a Java software module that may run on a NetWare or as a service on a Windows NT/2000 Server. The subscriber is responsible for receiving software distributions from distributors or parent subscribers. The subscriber also calls TED agents, when appropriate, to perform additional actions on the distributions after they are received. Parent subscriber. A Java software package that runs on a NetWare or a Windows NT/2000 Server. This module fulfills two purposes. The parent subscriber is first a subscriber and can receive and extract distributions for the server on which it resides. However, it additionally has the responsibility of forwarding some distributions on to other subscribers, when instructed. This module is the same software as the subscriber; the only difference is that the requests sent to parent subscribers have additional information that instructs the subscribers to act as parent subscribers and pass the distribution on to at least one other subscriber, thus reducing the number of subscribers to which the distributor must actually pass the software. This means any subscriber can become a parent subscriber by simply listing it in the routing hierarchy on a distributor object, or by listing it as a parent subscriber in any subscriber object. Routing Table. Each distributor has a routing table that contains a hierarchical list of subscribers who can receive distributions, as well as pass them on to other subscribers. TED agents. These are Java modules that are started by the distributor or the subscriber and have a specific function. For example, there are agents whose job it is to collect files and collapse them into a distribution package suitable for transmission to subscribers. There are also agents who are responsible for expanding these distributions and placing the extracted files on the servers that have received the distribution. Certificates. Distributors create certificates to provide secure distributions by issuing them to all subscribers receiving distributions from that distributor. For a subscriber to accept distributions from a distributor, it must have a certificate in its security directory from that distributor.
In ZENworks for Servers 3, the distributor and subscriber are the same Java software component. Whether the component behaves as a logical distributor, parent subscriber, or subscriber depends on the function that it must currently perform. Several logical TED components may reside on the same server. For example, you may have a server that is both a distributor and a subscriber, and agents when creating and extracting files from a distribution. eDirectory Objects TED uses objects in the directory to help direct and control its configuration and behavior in the network. The following objects are associated with TED components: Distributor object. This object may be placed anywhere in the tree and holds the configuration information for the distributor. Subscriber object. This object contains some configuration information that the subscriber uses. This object is never actually accessed by any subscriber (removing the need for a subscriber process to access eDirectory); instead, the distributor reads the configuration information from the subscriber objects and sends this configuration information to the subscriber agents with every distribution. External subscriber object. This object refers to a subscriber that is outside the distributor's tree. The configuration information for this subscriber is contained in a subscriber object in its own tree or in a local configuration file. This object is used to enable TED to distribute across tree boundaries or to servers that are not in any tree. Subscriber Group. This object represents a set of subscriber objects with common channels. You can configure the channels for the subscriber group and then assign subscriber objects as members of the group to share the channels. Distribution object. This object represents the collection of files that you want to transmit as a bundle across the network to various subscribers. A distribution is owned by a single distributor. That distributor is responsible for collecting, packaging, and distributing all the files listed in the distribution object. Channel object. This object represents a set of distributions and subscribers that are grouped together. When you place a distribution into a channel, all subscribers associated with the channel receive the distribution. When you place a new subscriber into a channel, all distributions associated with the channel are sent to the subscriber.
When you install TED components, you can specify which servers in the network will be distributors and subscribers and their relationship with any channels. The channel relationship can also be constructed after the installation process through ConsoleOne. The following list describes the relationships of the various components of TED: Distributors create certificates and copy them to subscribers for distribution security. Distributions are built on the distributor server. The same distributor sends the distribution to any of the subscribers (or parent subscribers) that will be receiving the files. Subscribers subscribe to channels to obtain distributions. A subscriber subscribes to many channels and receives all the distributions that are placed in each of the channels. External subscribers are subscribers that subscribe to a channel in an eDirectory tree to which they do not belong (that is, to the tree where they get their configuration information). Parent subscribers are identified either as a parent in the routing hierarchy list in any distributor object or as the parent subscriber in any subscriber object. Channels are collections of distributions and subscribers. Subscribers and distributions are associated with the channel. Essentially, the channel describes a set of subscribers that should receive the set of distributions. Distributions from many distributors can be placed in a single channel. Distributions are collections of files that are sent in the TED system. Each distribution belongs to a single distributor and can be placed in multiple channels. A distribution may be placed in any number of channels, and the distributor is responsible for sending the distribution to all the subscribers that are subscribed to the channels.
TED also uses digital certificates and message digests of the distributions to verify the contents and originators of the distributions. When a distributor is doing the gathering process (that is, the agent is actively collecting the files and placing them in the distribution file), it runs a message digest on the distribution. When the distributor is sending the distribution, it sends a header to the subscriber that includes the digest and other information all digitally signed with the distributor's signature. When the subscriber receives the header, it checks the distributor's digital signature with the digital certificate that it has for the server. (You need to install this certificate on the subscriber through ConsoleOne or manually.) If the signatures match, the subscriber proceeds with the download. When the download is complete, the subscriber runs its own message digest on the file and compares the results with the digest the distributor placed originally in the header. If they match, the file is deemed valid and the subscriber proceeds to schedule the agents to handle the unpacking of the distribution. |
