Traffic Server Components; The Traffic Server Cache; The Adaptive Redirection Module (Arm); The Host Database - HP P4535A - Web Cache Server Appliance Administrator's Manual

Hp cache server appliance administrator guide
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Chapter 1

Traffic Server components

Traffic Server consists of several components that work together to form a web proxy cache you can easily
monitor and configure. The main components are described below.

The Traffic Server cache

The Traffic Server cache consists of a high speed object database called the object store. The object store
indexes objects according to URLs and associated headers. Using sophisticated object management, the object
store can cache alternate versions of the same object, varying on spoken language or browser type, and can
efficiently store very small and very large documents, minimizing wasted space. Once the cache begins to fill,
the Traffic Server mobilizes garbage collectors to remove stale data, ensuring that the most requested objects
are kept on-hand and fresh.
Traffic Server is designed to tolerate total disk failures on any of the cache disks. If the disk fails completely,
Traffic Server marks the entire disk as corrupt and continues using the remaining disks. If all of the cache disks
fail, Traffic Server goes into proxy-only mode.
You can partition the cache to reserve a certain amount of disk space for storing data for specific protocols and
origin servers.
The Traffic Server cache is described in more detail in
RAM cache
Traffic Server maintains a small RAM memory cache of extremely popular objects. This RAM cache serves
the most popular objects as fast as possible and reduces load on disks, especially during temporary traffic
peaks. You can configure the RAM cache size to suit your needs.

The Adaptive Redirection Module (ARM)

The Adaptive Redirection Module (ARM) is used in transparent proxy caching to redirect intercepted user
requests destined for an origin server to the Traffic Server. Before the traffic is redirected by the ARM, it is
intercepted by an L4 switch or router.
To redirect user requests to Traffic Server, the ARM changes an incoming packet's address. The packet's
destination IP address is changed to the IP address of Traffic Server and the packet's destination port is
changed according to the protocol used. For example, for HTTP, the packet's destination port is changed to
Traffic Server's HTTP port (usually 8080).
The ARM supports automatic bypass of sites that do not function properly with proxy caches.
Traffic Server can respond to client request overloads by forwarding requests directly to origin servers. This
feature is called load shedding. Overload conditions, such as network outages, misconfigured routers, or
security attacks, can slow down Traffic Server's response time. In transparent configurations, Traffic Server
can use its ARM bypass functionality to forward overload requests directly to origin servers, bypassing the
cache. When the overload condition dissipates, Traffic Server automatically returns to full caching mode.

The Host Database

The Traffic Server host database stores the Domain Name Server (DNS) entries of origin servers to which
Traffic Server connects to fulfill user requests. This information is used to adapt future protocol interactions
to optimize performance.
Among other information, the host database tracks:
DNS information (for fast conversion of host names to IP addresses)
The HTTP version of each host (so advanced protocol features can be used with hosts running modern
servers)
Chapter 8‚ Configuring the
Overview
cache.
3

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