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Chapter 1
Overview
Traffic Server as a web proxy cache
As a web proxy cache, user requests for web content go to Traffic Server on the way to the destined web server
(origin server). If Traffic Server contains the requested content, it serves it directly. If Traffic Server does not
have the requested content, Traffic Server acts as a proxy, fetching the content from the origin server on the
user’s behalf, while keeping a copy to satisfy future requests.
Traffic Server provides two proxy caching options:
•
Transparent proxy caching, where user requests are automatically injected into a Traffic Server cache on
their way to the eventual destination. Users request Internet content as usual without any browser
configuration and Traffic Server automatically serves their requests. The user’s client software (typically
a browser) is unaware that it is communicating with Traffic Server. Transparent proxy caching is described
in more detail in
Chapter 3‚ Web Proxy Caching
.
•
Explicit proxy caching, where the user’s client software must be configured to send requests directly to the
Traffic Server.
Traffic Server as a reverse proxy
As a reverse proxy,
Traffic Server is configured to be the origin server the user is trying to connect to (the
origin server’s advertised host name resolves to Traffic Server, which is acting as the real origin server). The
reverse proxy feature is also called server acceleration. Reverse proxy is described in more detail in
Chapter
5‚ Reverse Proxy and HTTP Redirects
.
Traffic Server in a cache hierarchy
Traffic Server can participate in flexible cache hierarchies, where Internet requests not fulfilled in one cache
can be routed to other regional caches, taking advantage of the contents and proximity of nearby caches. In a
hierarchy of proxy servers, Traffic Server can act either as a parent or child cache, either to other Traffic
Servers or to other caching products.
Traffic Server supports the standard Internet Cache Protocol (ICP) to interoperate with existing ICP cache
hierarchies.
Hierarchical caching is described in more detail in
Chapter 7‚ Hierarchical Caching
.
Traffic Server in a cluster
Traffic Server scales from a single node into multiple nodes that form a cluster allowing you to improve
system performance and reliability. Traffic Server detects the addition or removal of nodes automatically. If
Traffic Server’s virtual IP failover option is enabled, Traffic Server maintains a pool of virtual IP addresses
that it assigns to the nodes of the cluster. Traffic Server can detect hard node failures (such as power supply
or CPU failures) and reassign IP addresses of the failed node to the remaining operational nodes automatically.
Traffic Server has two clustering modes:
•
Management-only mode, where you can administer all the nodes in a cluster at the same time. Nodes
automatically share configuration information.
•
Full-clustering mode, where the node caches act as a single aggregate cache. A Traffic Server cluster
distributes its cache across its nodes into a single, virtual object store, rather than replicating the cache node
by node.
A fully clustered Traffic Server provides a single system image to both users and administrators, appearing
as a single virtual server. Full-clustering mode includes management-only mode.
Traffic Server clusters are described in more detail in
Chapter 6‚ Traffic Server Clusters
.
