IT_001：IT 概念

1. End-to-end connectivity：端到端的连接。
   A property of the Internet that allows all nodes of the network to send packets to all other nodes of the network, without requiring intermediate network elements to further interpret them. 详见 http://en.wikipedia.org/wiki/End-to-end_connectivity。


2. Failover 和 Failback：故障转移和故障恢复。
   The failover operation is the process of switching production to a backup facility (normally your recovery site).
   A failback operation is the process of returning production to its original location after a disaster or a scheduled maintenance period.详见 http://publib.boulder.ibm.com/infocenter/dsichelp/ds6000ic/index.jsp?topic=/com.ibm.storage.smric.help.doc/f2c_pprcfailbackov_1v262p.html。


3. Middleware：中间件。
   Middleware is the enabling technology of enterprise application integration.
   It describes a piece of software that connects two or more software applications, allowing them to exchange data.详见http://en.wikipedia.org/wiki/Middleware。


4. Server affinity：
   A concept in load balancing and clustering.
   Server affinity refers to the ability of a load balancer or router to send a user's request to the same server where their session was initiated.
   If session-failoveris supported by the application or networking layout, server affinity is not required, as it doesn't matter which server serves the request.
   If session-failoveris not supported, then to support HTTP sessions, it is important to send the user to the same server for each request. Otherwise, the user will be forced to initiate a new session each time they are sent to a new server. This may for example, force the user to log in again, for every server in the cluster.