Glossary

bastion hosts

Well-fortified servers running initial point of contact protocols, such as HTTP or SMTP.

hash

Hashing is a scheme for providing rapid access to data items which are distinguished by some key. Each data item to be stored is associated with a key. A hash function is applied to the item's key and the resulting hash value is used as an index to select one of a number of "hash buckets" in a hash table. The table contains pointers to the original items.

idempotent

A function is idempotent if repeated applications have the same effect as one.

load balancers

Balancing, failure detecting, multi-layer (OSI network reference model layers 2-7) switches which can detect failure of clustered mid-tier servers and route around the failed servers. Load balancers also allow mid-tier servers to be taken out of service gracefully. Once out of service, a mid-tier server may be reconfigured or simply rebooted in order to reduce the chance of a crash or slowdown due to resource leaks and other bugs. Example are Cisco's CSS 11000 or F5's BigIP.

pool

A collection of instances of an expensive resource, such as a database connection-session pair, that can be used sequentially by different clients.

serial reuse

Several clients taking turns at using a resource. At any time only one client is using the resource, and only when the client is done with the resource will the resource be used by another client.

stateful inspection

A security system in which a firewall keeps track of various sessions by protocol and ensures that illegal protocol transitions are disallowed through the firewall. This blocks the types of intrusion which exploit illegal protocol transitions.

stateless

Absence of per-client state in a resource. For example, a database connection or session is stateless when all the client database updates have been committed or rolled back.

throttling

Controlling the maximum usage of a shared resource. Throttling is important when the resource is shared by many different applications, and you want to be able to guarantee decent response times for some class of applications or clients.